Battery Longevity
- Thread starter Charmet37
- Start date
Sure, measure the voltage over time to see how much self discharge it has. Self discharge with a healthy battery is usually a lot less than the parasitic draw of a semi-modern, meaning even 30 year old, vehicle. However if the battery was disconnected from the vehicle and kept float charging, might last a decade or longer as long as the float charge isn't set too high and it outgasses too much. On the other hand, I very vaguely recall once reading something about plate deterioration if there's not a little vibration from time to time.
f355spider
$50 Site Donor 2026
+1. Any of my cars or truck that sit for more than a week I leave on a Battery Minder or Pulse Tech battery maintainer. If you use the ring mount adapters they come with, and thread them through the grill of the car, makes for connecting them a simple matter. On one car I had to get more creative, but using the ring mounts makes it a few seconds to connect and no having to open the hood even.Forum needs a search feature because I am certain that many many years ago, someone posted a similar topic.
Then it happened again a dozen more times.
Don't leave a vehicle sitting for weeks, let alone months with the battery connected unless it's on a float charger. Anything PCM controlled plus minor other amenities like a radio that stores clock and station memory is going to average tens of mA constant current draw, which adds up over time. Disconnecting the battery can make a big difference due to that, but I still wouldn't leave a flooded lead acid starter battery sitting without a top-off charge for more than ~3 months at a time.
Lifespan and environment isn't the factor in this topic as much as that, although the OP did have a 7 y/o battery so factor for that as well. Short trips aren't so much either, unless talking about quite a few per day. Healthy battery, starter, and engine that fires right up in ~4 seconds will have put the current it drew out of the battery to start the engine, put back into the battery within single digit minutes, at least up to the level the vehicle manufacturer set it to maintain based on the smart or lack thereof charging designed into the vehicle, but it is still a little wear every time you start the engine, yet it is easier to start an engine that is already warm from the past trip driven, and the battery is nearer peak voltage the more recently it was driven vs sitting for days or more. Many different variables.
I currently have a float charger hooked up to an old vehicle that is seldom driven, and it's not even in my garage. I used about 40ft of reclaimed CAT5 ethernet cable, long enough to reach the trickle charger in the garage. It's wired to a cigarette lighter outlet plug, and fused at both ends. Actually triple fused if you count the lighter outlet fuse too.
You might wonder if it's low enough gauge for that, but with 8 conductors, 4 in parallel for positive and 4 for negative, it does fine supplying the tens of mA to float charge. The resistance of it isn't significant at a current that low. I'm more concerned about UV damaging the insulation over time, but I have a pile of old cable and can just build a new one in 5 minutes if that day comes.
Batteries last 1 month more than the warranty date. Test 1 month before the warranty date.
With a modern car you don't want an iffy battery. Too many computer controlled things rely on a.steady and correct voltage. Plus, our computer controlled engines are so good at starting that a battery can fire up the car one day, and not the next. Happened to a friend recently on a Cooper with a 5-year old battery. Just died enough overnight to change from go to no-go. Triple A refused to attempt a battery replacement since that thing is so buried in a Cooper.
High temperature is a big killer of batteries and not just from the climate. A battery with no thermal insulation and exposed to engine heat will not last as long as a battery mounted elsewhere such as behind a sealed and insulated bulkhead.
Patman
Staff member
One feature of new cars that really bugs me is that when you shut them off the headlights stay on for too long. That certainly is going to reduce the life of the battery. So in both of my cars if the headlights stay on once I shut them down I manually turn them off.
Is that an indicator of OEM battery quality or an indicator of how the battery was treated or rather misgtreated from when it left the factory to point of sale. I can't imagine they would think of charging the battery if a long time elapsed between factory and sale. The mentality will be if it starts the engine then it's fine and if it doesn't start then jump it but don't bother charging it properly.
f355spider
$50 Site Donor 2026
True about cars not liking a weak battery...some cars will start throwing phantom codes and stuff when that happens.
But many battery failures can be detected before they leave you stranded. I test the battery on my Tundra at each oil change, which due to driving 100 miles 5 days a week, is about every 3 months. Tested fine at previous oil change, then at next one it says "replace"...yet it started and drove just fine. No sign of a slow crank. I replaced it that day.
f355spider
$50 Site Donor 2026
My 2018 BMW has the "welcome home" headlight timer, it also has shutters on the grill that open and the electric cooling fan continues to operate for several minutes after shut down to cool the engine (twin turbo V8). Aux coolant pumps run as well to cool the turbos.
BMW's solution is to use two batteries. An H9 105 AH starting battery in the trunk and an aux H5 60AH battery in the engine compartment. The aux battery powers the car, anytime the engine is off, including during the "start stop" mode. Probably why this car has a 230 amp alternator...
