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Issues arising from installing a battery with a 'group size' different from manufacturer recommendat

Our minivan suffers from non-recoverable engine problems, but I put a Bosch battery, group 65, with CCA 850 only a month ago. I hate to loose my investment in that battery when we sell the minivan for parts! Our other car is a '03 Subaru Forester, which takes a group 35 battery, and I considering whether I might transfer the new minivan battery into the subaru. I’m aware of some of the issues, but I’d like your opinions of whether it is technically ok and safe.
Here’s what I know. The group 65 battery has the ‘+’ terminal on the left, while the group 35 battery has the ‘+’ terminal on the right. Isn’t it ok to turn the group 65 battery around (180degrees) which puts the ‘+’ terminal on the correct side, altho about 3 inches closer to the firewall. (I haven’t yet checked to see whether the terminal cables will be compatable with this slightly different location.)

The group 65 battery weights 10-lbs more, but I don’t think that’s an issue.

The group 65 battery is 2-1/8 inches wider, one half inch deeper, but 1-3/8 inches shorter. I believe I have to be concerned whether cooling air flow is reduced by this different battery profile. I believe I have to be concerned whether the existing securing strap for the taller group 35 battery can be cranked down the extra 1-3/8 inches to tightly grip the group 65 battery. Do you have any experiences about these issues?

Is there a matching of charging capacity of the alternator with the battery that might make replacing a group 35 battery of 640 CCA with a more powerful group 65 battery with 830 CCA?

What do you think? I hate to waste a 1 month old, powerful battery when I might be able to use it in my remaining car.

The battery is too big for the space in the Subaru but if you are able to get past that obstacle then the electrical requirements do not matter. All 12v batteries are the same in the eyes of the car’s electrical system.

when you junk your minivan, if you are allowed to keep the battery, do so. if you can wedge this thing into your car…great. there are no real issues as 12 volts is 12 volts. the problem may be more along the line of wedging this thing into the space. you really don’t want to change the location of everything else.

so pass on the ordeal if it isn’t a simple drop and secure the battery. once you talk about getting cable extensions/re routing the battery…essentially you have lost of savings and/or safety.

some people like to extend their life of the battery by routing it to their trunk. the safety of a chord running thru the middle of the passenger compartment is not safe at all.

don’t be foolish and put people at risk.

I usually find that a different group size battery will rarely fit in a vehicle that requires a different group size. Especially if the battery is larger.

It usually won’t fit in the battery tray, the hold-down can’t be used, and if the battery is turned 180 degrees the cables won’t reach the posts.

My son-in-law removed a nearly new battery from the vehicle he sent to the bone-yard. This battery wouldn’t fit in his replacement vehicle nor does it fit in any vehicles that required a battery that came into the shop. So it’s still sitting on the shelf.

It’s better to stick with proper group size battery for the vehicle.


FIT is the only issue with bci group size.
But as others have stated , that alone entails many perameters, some minor some major.

  • It needs to mount solidly to the tray. Don’t just sit a larger battery on top of the smaller tray. A wobbling battery can cause problems that wouldn’t otherwise exist…like…acid spill, ground out short, wire breakage.
  • Some have a cover that serves a purpose.
  • Even if the cables reach to the other side watch out for short to ground. You’ll put the positive terminal too close to body work and wobble, cable rub and jump starting can easily touch ground.

We had one in the shop…the customer put in one too TALL…looked just fine …with the hood open…( you know where this is going don’t you )…then they closed the hood…bzzzzt !

Some vehicle lines have optional sizes and some battery trays are built with room to change…but you need to prove this before substituting.

The only easy upgrade is when the car came with a tray that’ll fit a larger optional battery, like for a larger engine or some option package.

Back in 1962, I bought a 1947 Pontiac for $75. The car was supposed to have a long, narrow rectangular battery. However, a previous owner had put in the cheapest battery he or she could find. It was a square battery that said “Recommended Only For Warm Climates”. A square board was placed on the battery tray and a stout wire covered with a section of heater hose was fed through two holes in the fender liner to hold the battery in place. It worked. I never changed the battery, and surprisingly, it started the car in zero degree weather.
Electrically, there is no problem. It is the physical fit that is important.

It is the physical fit that is important. Well said @Triedaq .

I always buy the biggest battery that will fit in my vehicle. I’ve always done this and never had a problem but I would never try to change the location of the battery terminals. Never.

As long as the battery has the cold cranking amps you need, any 12 volt car battery that fits will work.

Sell the battery, it is too much of a pain to install it in your car. It won’t hurt anything, it is just a pain to adapt it.

If it will physically fit and the leads reach without stretching or damage, half the battle is won. There IS concern for the charging system if the battery is upsized too much (or downsized too much), but in this case, shouldn’t be an issue.

Details: upsizing too much can lead to charging current out of the design range for the alternator/regulator, which can lead to early failure of the unit or inability to fully charge the battery.

Now that’s one I’ve never heard.

I just purchased a battery for my pickup. And I had the option of a 350 CCA battery up to a 750 CCA battery. Of course I opted for the 750 CCA battery as I live in Minnesota. The battery came with no warning that the charging system must sized to the battery CCA’s.

I’ve purchased alternators that came with warnings about the battery needing to be charged to 12.4 volts or more before putting the alternator into service or alternator damage can occur.


Details: upsizing too much can lead to charging current out of the design range for the alternator/regulator, which can lead to early failure of the unit or inability to fully charge the battery.

I believe this is incorrect. The battery will only draw what it needs to recover what it has expended starting the engine, which will be roughly the same regardless of battery size.

Thank you to all who took the time to share your experience and knowledge with me. “enlpublic” did confirm my fear that there might be a mismatch between the alternator/regulator and the battery. “Mustangman” is probably right that I should sell the battery separately so someone with the appropriate car, needing a group 65 battery, can benefit from the battery. And for me, I avoid the risk of damage to my remaining car and the loss of time attempting a tricky adaptation.

Yep, sometimes you just close your eyes, take the hit, and move on with your life.