My neighbor heads to Alaska
every year in his 50' Californian.
Two years ago, he replaced all ten of his ten year old Interstate 220 aH 6 volt batteries just to make sure he'd not have a problem while cruising.
They've been well cared for and had an automatic watering system in his boat.
He gave them to me for the core
After making sure they were all charged and performing a load test, I put them into service
in my home's backup power system.
I had to replace only one of the batteries and I bought a Costco golf cart 220 aH.
They are in a series parallel arrangement and all are still holding up nicely.
After disconnecting all of them yesterday, I again performed a 50 and 100 amp load test.
There are only a couple of them that are beginning to get a little 'squishy'.
All held their voltage nicely for a couple of days before the test was performed.
I used my Fluke Scopemeter to grab the Max, Min, Average and Now voltages on each battery.
With a 50 amp load for 5 seconds, the worst one dropped about a half a volt.
The best one was about 0.25 volt drop.
With the 100 amp test, the best pair dropped 1.2 volts.
My new 200aH LiFePo4
batteries on the boat were also tested at 100 amps for 5 seconds. The voltage drop was 0.4 @100 amps and that might have been due to the 1 gauge connector in between the two pairs in the installation
Gotta love those new batts !!!