One of my start batteries is slowly dyeing they are the big 8da b batteries, my question is should I just replace the bad one or replace both? I have heard in the past you should replace both, the bad one was new in 2005 the other one is newer it does test real good but I cant find a date on it. I suppose it is three to four years old, Just curious what you guys recommend. Thanks.... John.
Always use batteries in a set with the same date codes.
Lifeline for example will replace a set even if one fails during the warranty period.
For maximum capacity and battery health - it's best to replace both... but it's not the end of the world if you don't.
The older battery's condition will bring down the newer battery.
If your situation is something you need reliability on for lots of starts - best to replace both, for sure. If it's not, it's up to you if the cost savings is worth the risks of prematurely aging the newer battery. If you're not starting often, it may not be much of a noticeable concern.
- Cherie
2005...Mine are 2008's and I would not even consider buying one...
If they have not received equalization charges on a regular basis.....
then I absolutely would not buy one....My inverter charger guru/yoda says MONTHLY Equalization is best. (I don't listen well) I do mine quarterly to bi-annually as they age.
And 8 years is long and fruitful life...for a battery.
For a more targeted way of dealing with one weak battery, try to find out if you have hydrometer readings that show a low cell.
I have had no luck with a battery that shows a low cell.
If they are near even, I would try a desulfater. We have recovered many batteries this way.
A desulfater will desulfate an 8D in three or four weeks when used with a one amp charger. The voltage will gradually rise until it starts to fall. If it is up to 14 volts, you should get quite a bit of use out of the battery.
Good luck.
Tom Caffrey
I have 2 group 31 start batteries for our 8V92TA engine. When one went bad I took both to the battery store to be tested, one was still good, so I bought another used one to go with the one that tested good. They have been starting the engine well for more than 2 years. The used battery cost $40. If you can find a good used battery you may have the same experience.
Good luck, Sam
I had to replace my 8D start batteries. So I went to Walmart and bought 2 of their biggest batteries. I think they where 800cca and half the size and weight of the 8D's. Been 3 years since I have replaced them and still no problems. If i did have a problem there is always a Walmart right down the road no matter what part of the country you are in. At least the most part!!!! But always replace in pairs. Then save your good one for a spare for your genny.