Trickle-charging, Maintaining & Replacing your 124 Spider Battery

Go directly to:   Other Battery Info         Alternative Lightweight Battery                                           Effects of the Security Alarm System & Solar charging                                                        Replacement Batteries


[UPDATED 9/30/2019]
Keeping your car battery trickle-charged during the winter season is much different than charging a battery that is discharged and unable to start your vehicle.  Not only are the charging devices different, but so too are the battery connection procedures.  Battery chargers should only be hooked to your battery posts using clamps (red to the  + post and black to either the post or a good ground connection on your engine or car body) and should never be used for extended periods of time to “keep your battery charged”.  That is the job of a trickle charger or a battery tender.

Battery cells should be charged gently so that there will be no chance of immediate gassing and temperature rise over 100°F.   Regular battery chargers supply much more current, which if not regulated properly causes high temperature rise and excessive gassing resulting in heavy loss of water, leading to permanent damage to the battery cells.  During charging of batteries, continuous monitoring is required, if gassing starts and the temperature reaches the said limit, reduce the rate of charging. If after reducing the charging rate, the temperature is still approaching to the limit, it indicates the completion of charging process because even the normal rate of charging may produce high temperature rise if the battery approaches to the fully charged condition.

There are several other manufacturers and brands of battery tenders, but just like everyone associates the word Kleenex® no matter who made the facial tissue they’re holding, Deltran’s “smart” Battery Tender® trickle chargers are the most commonly known brand. Battery tenders are gentle trickle chargers that have circuitry designed to prevent the battery from being overcharged, which could kill your battery over a period of 2 or 3 months.   Like charging your phone from a USB port on your computer rather than a dedicated 2 amp charger, battery tenders’ low current output may be unable to bring a dead battery back to full capacity; that is the job of a dedicated battery charger.  Since the current flow is much lower, a battery tender doesn’t have to be hooked up directly to your battery posts, although that still is the most preferred method.

Battery Tender® trickle chargers usually come with a SAE standard “disconnect“, so that different harnesses can be attached, depending on your specific needs.  The preferred option is to install the battery to port harness to your vehicle, and simply attach it to your 12 volt disconnect port when put into use.  The temp clamps are another alternative, but the clamps could undo themselves or prevent you from closing your hood, etc.  Gasses are emitted during charging and you don’t want to risk causing sparks near the battery!

Cigarette lighter receptacles used to be a convenient access point for battery tenders, but they usually are no longer “hot”, meaning they are only ON with the Ignition in the Accessory or ON position, rather than all of the time.   Besides, access to our receptacle is very awkward due to it’s placement.

The OBDII plug (at the bottom of your dash panel to the left of the steering column)  on the other hand is usually “hot”, so it makes for a convenient hookup point to the battery, but only for trickle charging – not for rapid charging of a dead battery!  In fact, trickle-charging via the OBDII connector is now the common method for auto technicians to keep 12 volts on your various modules and the Infotainment system while servicing your battery, so that you won’t be inconvenienced with losing all of your radio station settings and your emissions testing readiness.

So, as a third alternative for those using a Battery Tender® during the winter season, consider purchasing their optional polarity-correct OBDII connection cable, shown in the photo at the top of this article.   Want to be able to charge your phone while the vehicle is not in ACC or ON mode?   As long as you already bought the OBDII cable, and again, since the OBDII plug is “hot”, you can purchase their USB 2.1 amp charger that plugs into the SAE disconnect, and it will charge your USB device while the vehicle is OFF.  They also sell a female cigarette adapter that plugs into the SAE disconnect that again, will be on all of the time.


I am not affiliated with Battery Tender®, just an admirer of their product offerings and hopefully this article helps some of my blog readers make the correct decisions involving battery charging.

81ak2bxzs3jl._ac_sl1500_The trickle charger I ended up ordering though, is the NOCO 5-amp Genius5 fully automatic charger, since it is in a sealed plastic unit (much safer when sitting under the hood near the battery) with LEDs that inform you of what it is doing, and is designed for 6-volt and 12-volt lead-acid automotive, marine, and deep-cycle batteries, including flooded, gel, AGM, and maintenance-free, plus lithium-ion batteries.  It is an all-in-one solution – battery charger, battery maintainer, trickle charger, plus battery desulfator.  There is an optional OBDII adapter cord available too, that can be used as a battery maintainer while replacing your battery, and also allows you to charge your battery without opening the hood.

Other battery info + maintenance

fiat battery 37 point 35 lbs vs Miata battery 25 point 15 lbs.jpg

Fiat 124 battery                                            Mazda MX-5 battery (w/o i-stop)

cold start disableApparently if you attempt to start the vehicle and the ambient temperature is below -22ºF  (-30ºC), the ECU module will prevent the starter from engaging with the engine, as indicated to the driver by a flashing yellow “Cold Start Disable Indicator Light”. However, between that limit and the +teens (ºF) are some very cold temperatures, and starting your vehicle on those days is when you’ll really count on the Cold Cranking Amps (CCA) that your battery is capable of.


Mazda’s “Start-Stop” battery (Panasonic EFB — enhanced flooded cell lead-acid battery) used in the 124 Spider (at least for MY 2017; I’m not sure about subsequent years), is pricier, much heavier, and capable of about 50% more CCAs (520) than the standard lead-acid batteries used in the MX-5 ND (350).   Perhaps Fiat concluded that Mazda was a little too aggressive in their gram strategy, at the expense of reliability (the manual transmission in the MX-5 is 15 pounds lighter than the Spider’s, and we now know that it hasn’t stood up to aggressive driving very well), and chose to install the heavy-duty battery instead.

b26f-d005-4fff-a2d6-8f5aa047785dThat whirring sound you hear when the engine is switched off are the current-drawing motor(s) that may run for up to around 15 minutes after the engine has been stopped and could somewhat deplete a smaller capacity battery.

  • An electric auxiliary water pump insures proper cool-down of the turbo bearings by circulating coolant through the turbo, after the engine is stopped.
  • Additionally, if the coolant temperature is above 223º F, the radiator fan will also run after the (hot) engine is stopped to aid in bringing the coolant temperature down quicker.
battery weight

photo courtesy of zonker

The battery is designated a Q85*, 520 CCA, 65 Ah [20 hr rate], 52 Ah [5 hr rate], and weighs 37.3 lbs (16.9 kg).   It is a serviceable “Wet Cell” (flooded with electrolyte, which is sulfuric acid and distilled water), Lead-Acid battery with six exposed, threaded, vented caps (as compared to the MX-5’s 25-pound, “Maintenance Free” type with six recessed, threaded, sealed caps).   This merely means that it is much easier to monitor the electrolyte levels in the individual cells  by unscrewing the caps and looking into the cells (with good lighting available), at least once per year:

  1. If the electrolyte level inside the battery cell comes down, it must be replenished with distilled water (not tap water which has calcium and many other minerals) up to the level marked on the cell itself. This is to compensate for the loss of water due to evaporation.  The lead plates within the battery should always be completely submerged in electrolyte – hence the term flooded.
  2. While topping-off cells with low electrolyte levels, insure that the level in the battery cells not exceed the fill-level line. Otherwise there may be a chance of  electrolyte overflowing during gassing of the battery, which besides being very corrosive, could cause softening of the sealing compound on the top cover and subsequent leakage/contamination of  electrolyte.

stevet wrote a good blurb regarding battery maintenance on 9/29/2019, that I thought I’d include here, even if it might be repetitive with stuff I wrote, because there are many younger drivers that are not even familiar with batteries requiring some maintenance:

This morning, I’ve done a few minutes of poking around the internet about car batteries that “still allow you to perform maintenance”. I worded that deliberately, because after those few minutes I’ve concluded that owning a car battery that allows me to check the water level, and add water as necessary, is not necessarily a bad thing. “Maintenance free” wet cell batteries may not be as maintenance free as we’d think, they may still have ventilation provisions built into them to allow charging gasses to escape (charging gasses being hydrogen and oxygen, which when combined were previously the water inside the battery electrolyte), but may not allow provisions to replace water that is no longer inside the battery (which also leads to a shorter battery life). Note the battery electrolyte does not go away, just the water component from the electrolyte recipe, water is what may need periodic replacement.

Wet cell lead acid batteries, while charging, can cause the water in the cells to separate into hydrogen and oxygen gasses, especially in overcharging situations. Other nuggets of info:

  • BE SAFE! Battery acid can blind you, burn you, and eat holes through stuff is splashes on. It’s ph level is less than 2, very acidic, very nasty. The sites below offer safety info. Protect yourself and your work area.
  • Your vehicle alternator doesn’t necessarily “charge” your battery as much as it maintains the full charge of the battery. Think trickle charger for a battery in storage. You’d use a separate full power battery charger to charge a battery that is, for whatever reason (such as low charge from long term storage), at a below-full-charge state.
  • In batteries that allow adding water, do not use tap water due to dissolved minerals and other materials that can be in the water, use only distilled water. It’s a buck a gallon at the grocery store.
  • Charge a battery only in a well vented area, remove all sources of spark or ignition (incl. the vehicle being shut off) to prevent explosion of venting hydrogen gas. (I was present for this event once, I never want to see it again.)
    -Make sure the battery is sitting level (achieve, if needed, buy driving onto scrap wood blocks or similar), clean the top of the battery and remove the caps from the tops of the cells. The water level inside the cells needs to at least cover the top of the metal plates before charging. Differing water levels in the cells is possible, they may not all be at the same level. The electrolyte can warm and expand during charging so do not fill the cells more than just over the top of the plates prior to charging. Leave the caps loose while charging to allow hydrogen and oxygen gasses to escape. After charging, add more water as necessary. Sites I viewed suggested anywhere from 1/2 inch of water coverage above the plates, to filling with water to touch the bottom of the cell vent/fill holes (see linked video).Video-


*  Q85 Specs


Replacement Batteries

In the coming years when it comes time to replace your battery, unless you are on a mission reduce your vehicle’s weight**, look for a 90D23 or 90D23L (Japanese standard) battery and know that it will fit in the factory designated location.

  • L is standard, don’t get R as the cables won’t align with the terminals
  • higher than 90 has even more capacity

I have heard reports that Group sizes 51R and H5 batteries fit nicely as well, and they are both spec’d at 500 CCA, which is very close to the Q85 (520 CCA), and are said to be available at much cheaper prices.  In very cold climate regions,  I would favor a battery with more CCA capacity, rather than less.

[UPDATE 12/3/2020]
In my opinion, we really don’t need to replace the battery with the same start/stop unit. The replacement just needs to (1) fit (post alignment and physical size), and (2) have adequate CCA capacity. Other than the Mopar H5 battery used in the Jeep Renegade (shown below), we are all awaiting feedback on other successful installations. The turbo cooler pump isn’t as big a concern as we all first thought, but it does equate to not going lower than 520 CCA.

[UPDATE 4/13/2021]
Julia DeGrace has installed a nice cost-effective Group 35 replacement battery (commonly available in the U.S. at AutoZones’ 6,000 locations) that fits nicely (better than the H5), and is more capable than the Mopar battery discussed below, a Duralast Gold Battery # 35-DLG, Group Size 35, 640 CCANext photos, courtesy of Brody, who also installed the same battery in October 2022.

I think we are all agreed now, that Group 35 is an ideal replacement battery for our 124 Spiders, although you may have a difficult time convincing the guys behind the counter that this is the battery of choice for our cars. 

Both John M. and Anclar have confirmed that the corrugated/insulated surround “battery cover” (Mopar # 68313904AA) accommodates the replacement batteries.  Do not discard, as it should be reused, in order to protect the battery from turbo/engine radiant heat.

[UPDATE 6/12/2021]
Karl Kramer has also installed an X2Power Premium AGM # SLI35AGMDP, Group Size 35, 660 CCA  (although $100 more than the Duralast) Group 35 replacement battery (commonly available in the U.S. at Batteries Plus Bulbs’ 720 locations) that fits nicely and is more capable than the Mopar battery discussed next.

FCA dealers are using “Maintenance Free” Mopar # BB0H5500AB (which is original equipment in the Jeep Renegade and others) as a good-fit replacement battery.  The battery tray will accommodate up to 9 ½” x 7⅛” max., and even though the battery is shorter, apparently there are enough threads on the J-hooks to tie-down the battery securely.  As booztedgt points out though, the heat shield sleeve won’t fit, and the negative terminal module will be a little crammed.

mopar battery BB0H5500AB

photo courtesy of magoffin – click to enlarge

[UPDATE 12/4/2021]
It appears that FCA now has a specific replacement battery for the 124 Spider, rather than using the Jeep Renegade battery shown above.  I think I see that the heat shield fits with this battery, and the 585 CCA exceeds that of  the original battery.  Mopar # BBQ85001AA

mopar battery

photo courtesy of Scott Mackie

battery comparison

photo/comment courtesy of booztedgt (added 7/10/2021) – click to enlarge

[UPDATE 3/12/2022] John sent me this today:

My battery research of a while back is now out of date.  Then local Mazda dealers said they sold the factory Panasonic battery.  Because my original 6 year old factory died suddenly last week, I found that Mazda dealers near me now only sell Interstate batteries (but with the original part number and very high price).  Because of good past experiences with Duralast batteries from Autozone, I bought the Duralast Platinum EFB Battery, 35-EFB Group Size 35, 585 CCA (shown below).  Perfect fit including sleeve, much less expensive, and plenty of power.


Note 1:  The ⊖ negative (see Note 3) or ⊕ positive terminal should always be disconnected from the battery, prior to working on any electrical/electronic components:
→ →• Tap the brake pedal afterwards, to completely discharge residual power
→ →• Afterwards, upon re-connection, all modules learn current configurations

SteveP adds this advice regarding the ⊖ negative terminal:

Right at the negative battery terminal there is a two wire connector with a push tab release (right where the tape is holding the wire conduit to the connector) – very carefully remove the connector from the negative battery terminal “battery sensor” before removing the negative battery terminal. The connector has two wires going to it – one gray, one a weird kinda pink. The sensor is fragile, so highly recommend you do this first. And, it’s best to disconnect the negative battery terminal before the positive, because if you try to disconnect the positive terminal first, and your wrench accidentally hits something metal – say the battery hold down bracket, or a fender, or something similar – there will be an instant and massive short circuit and most likely some damage.  If you disconnect the negative terminal and isolate it, there should be no pressing need to disconnect the positive terminal, although it won’t hurt, and if the negative terminal is not properly isolated then it may pay significant benefits! 

negative terminal

Not only is the sensor fragile, but it is also expensive (≈$500) and somewhat fragile, and if it breaks, an error code will occur , and the alternator will no longer charge the battery.  Also note that like most Fiat parts, your car could be un-drivable, since it could take a while for the dealer to locate a replacement for you.

battery sensor

Note 2:  Mazda’s Service Bulletin regarding the i-stop battery can be read here.

Effects of the security alarm system

If you have the standard immobilizer rather than the security alarm system with the microwave sensor (it’s located under the armrest tray), you probably don’t have a hood latch switch, unless you have a European car (it’s called a bonnet switch there), so you are able to leave the hood open when trickle charging using battery clamps and/or simply leave the vehicle for 2 or 3 months without even worrying about charging the battery.  I notice I have a harness going to my hood latch switch, but nothing is plugged into it, unlike the diagram below. 

Your car will not be able to go into sleep mode with the hood open, if the latch switch is wired in, resulting in a higher current draw that will deplete the battery quicker.


testing parasitic draw is in the “Battery Inspection” section of the service manual

I’m told any number of things can interact with the security alarm system’s microwave sensor, including a phone stored in (or setting on) that armrest tray, windows open, hood unlatched, a moth flying around in the car, and even an overhead ceiling fan can keep the security system from going into long-term sleep mode, resulting in a significant current draw which could result in a dead battery within a couple of weeks.

This would be the person that may need to seriously consider a trickle charger with the OBDII connector as discussed above!  (and perhaps consider disabling the microwave sensor as well)

Solar charging

If your vehicle will be stored in a location that lacks electricity, but is exposed to sunlight, you may want to consider solar charging your battery.  In addition to needing a solar panel, you’ll need a solar panel charge controller  connected either directly to the battery, or using the OBDII connector discussed above, which will control the rate of charging much like the trickle charger does, and it will also keep the solar panel from discharging the battery during the non-daylight hours when it is too dark for charging.

It is important that the battery voltage be kept up, as the life of the battery is significantly shortened, if allowed to get into the less-than-30%-charge zone, and you may not be able to replenish it back to 100% – ever.  By design (with regard to lead-acid batteries), only “deep-cycle” batteries are OK with discharging into the less-than-30%-charge zone.


Alternative Lightweight Battery

**  Good-Win Racing has a Weight Saving battery installation kit that accommodates the ultra light Battery Tender® LiFePO4 (Lithium Iron Phosphate) family of batteries (although I don’t recommend you install this type of battery for everyday driving).

battery-tender-batteryThe DELTRAN BTL24A360C, which along with all of the mounting brackets, weighs 3.35 pounds and replaces over 39 pounds of battery, tray, surround and mounting brackets.  At 360 CCA, I don’t know if it would serve your needs on the coldest of winter days or not.

The DELTRAN BTL35A480C weighing 1.15 pound more and capable of 480 CCA (vs. 360 CCA), is Good-win’s recommended weight-reducing battery for the 124, because of current-drawing motor(s) that may run for up to around 15 minutes after the engine has been stopped as well as the parasitic drain of other always-on electronic modules like keyless entry and the anti-theft alarm system.  Bulldog66 shared his short-lived experience with this battery in his 124 Spider, and came to the conclusion that the battery aligns more with racing rather than average irregular driving, and he ended up putting the factory battery back in.

If you go this route, you’ll need a pair of  post adapters  with M6 threads so that the harness will attach conventionally to the battery without modifications.

By switching your aluminum alloy wheel rims with premium magnesium alloy rims that are at least 10 pounds lighter each, along with this lighter battery, you could knock 75 pounds off of your 124 Spider in one day 😉 , but my advice for most people is to stick with the OEM battery.

8 thoughts on “Trickle-charging, Maintaining & Replacing your 124 Spider Battery

  1. I added a section for Replacement Batteries today, and altered the title to reflect that. I didn’t think all of the suggested batteries should be part of the Specs page, so a link is there instead. When it is time to replace my battery, I think I’ll be heading to Autozone 😉


  2. John M. sent me an update, which I’ve added to both of my Battery articles.

    My battery research of a while back is now out of date. Then local Mazda dealers said they sold the factory Panasonic battery. Because my original 6-year-old factory died suddenly last week, I found that Mazda dealers near me now only sell Interstate batteries (but with the original part number and very high price). Because of good past experiences with Duralast batteries from Autozone, I bought the one shown below. Perfect fit including sleeve, much less expensive, and plenty of power.


  3. After some recent confusion on the Fiat 124 Forum, Anclar cleared up the fact that the OEM battery cover fits with the replacement Group 35 battery. I added to the article:

    Both John M. and Anclar have confirmed that the corrugated/insulated surround “battery cover” (Mopar # 68313904AA) accommodates the replacement batteries. Do not discard, as it should be reused, in order to protect the battery from turbo/engine radiant heat.


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