I've got a chevy 7500 dump truck with Cat diesel. It has a pair of batteries. Just started going dead after sitting a few days. First thing I did was to put in a heavy duty battery disconnect, suspecting parasitic drain. That didn't help. I load test the batteries and one checks good, one indicates replacement needed. Do I need to replace both as a pair, or can I get by with just replacing the one that checks bad? Thanks, Greg
The short answer is to replace them in pairs. The long answer could be that if it is a truck that gets used very frequently and the good battery is not that old, you might get by with replacing the bad one. But if it sits a lot then one can drag down the other. But if you put an AC powered battery tender on it then it might be OK anyway. Not a completely straightforward answer.
If the both the batteries are the same age or you don't know when they were installed replace them both.
I don't know if it is true, but it makes sense, my battery supplier told me to do in pairs because the new one will do most of the work when you replace only one. Has to do with discharge rate and reserve capacity. Said the new one will have a shorter life. Maybe he just wants to sell batteries.
Both or none, it may start just fine with one battery, especially if you plug it in on the colder days, and for sure if you plug it in and add a battery warmer. If that one battery won't start it, then something is wrong. You can replace one battery, but you might regret it.
12 volt or 24 volt ,were the battery connections clean and tight? If not you may have been drawing more from one battery then the other.
I replaced them both. The old ones were Exide 31XHD. When I removed them they both had tags on the sides that said November 2016, so a little less than 3 years old. I've only had the truck a few months. One of the batteries still checked good and I should have kept it for some of the other equipment, but had to bring in the core to get the price on the new batteries. The truck doesn't get used that much, so hopefully with the battery disconnect, now, these will last. It's a 12 volt system and the connections were clean and tight. thanks for the advice, Greg
Those batteries may have still had some warranty left but replacing them isn't a big expense in the grand scheme of things.
Similar situation here. Two batteries from 2016 with disconnect switch, 500 cca each. Load test after a failed start showed batteries were equal. Replaced both because I'll not want to mess with them this winter. Got a new lesson with a Capacitance Test. Each battery was 12.2 V which charrted out to 200 cca each. Problem is that I used the machine less than 200 hour since since 2016. Maybe time for a battery maintainer.
Battery tenders/maintainers are the ticket! We use them on race and show cars all the time. I always replace batteries in pairs when they are paired. I also use CAT batteries in all heavy duty work. They seem to last longer than most others, even after abuse. Just my 2 cents
I use a separate disconnect on my dual batteries. One for each battery. Here in the cold country the bad battery usually drains the good battery and then that one freezes and breaks. I shut the switches off alternately when using them to insure both batteries get full charge. Of course this only works with batteries hooked in parallel's.
if two batteries connected in parallel are used, they should be replaced at the same time for maximum efficiency. they should be exactly the same-therefore they will have the same internal resistance and will be recharged at the same and equal rate. otherwise the battery with the least internal resistance will accept most of the charge if only being used for a short time assuming the connections and cables are good. if they are a matched pair they will both be drawn down at the same rate and recharged at the same rate.
Battery warranties are pro-rated. They use MSRP to calculate the warranty amounts. So if you are past 75% of the warranty period you usually end up paying for most of the battery anyway.
off the shelf batteries especially group 31 regardless of name brand have a 36 month life expectancy whether you use them or not.
why would they only last three years? Not doubting you, just trying to learn. Greg