starter battery EOL?

the signs

Last week I had one slightly slower crank when I started the van. For the past two nights I thought the keyfob power locking ker-chunking was slightly off. Easy to see in retrospect, but maybe not at the time.

the problem

Went to take doggo for a walk and tried to lock the van with the fob. No joy. I assumed it was the fob battery. Tried to hit the power lock button manually; also no joy. What?

Turns out the starter batt was quite dead after sitting for 12 days. I hit the combiner button on the Battery Doctor VSR which parallels the house and starter batts for 3 minutes.

the next morning

Hit the combiner again to give the starter batt another 3 minutes of love.

I pulled the battery cover from the floorboard, removed the restraining gear, and checked the cells. All the plates were covered with water. I noticed some fluffy white corrosion in the battery box which suggests the batt might be outgassing more than before.

I pulled the terminals and saw light corrosion on the NEG and more on the POS. Cleaned them both, greased, and sewed everything back up.

leaving them paralleled all day

I wanted to leave the starter battery connected to the house bank all day so it’d charge for hours. The way to do this is to show the VSR >13.4v on the input side (ie, start the engine).

observed current

Observed current going into the bank was 59.5A (.21C). Working backwards from the Victron data that appears to be ~40A from solar and ~20A from the alternator.

I let the engine run a couple minutes until the high (“choked”) idle came down to normal. I shut it down and the VSR remained connected as expected/desired.

planning for replacement

While it’s conceivable the clean-and-charge will buy a few more days of service from the starter battery I assume it’s EOL. I’m not mad; it’s the batt the van was built with in Nov 2016. So it’s 8.5 years old right now, and basically only gets charged every 14d when I relocate.

Looks like the Promaster Forum is walmart’s EverStart H8. The sealed FLA are ~$160 but out of stock. The AGM are ~$180 but in stock. I guess we’ll see what’s on the shelf when I get to Santa Fe later this week.

update the next morning

I tested starter batt voltage this morning: 10.55v. She dead.

The house power setup was up to 13.5v by that time and I used the Magic Button to combine the batts. The starter battery pulled 16A and rapidly tapered off. This tells me the batt is likely sulfated from age.

I allowed the combiner to time out then started the engine as before. After idle settled down I shut it off and will leave the starter batt charging from solar all day again. I don’t expect different results.