A year ago, my GMC was 5 years old. The dealer told me my battery had a full charge but failed the load test. That's when I bought the batteryminder. It can charge gel, flooded and AGM batteries at 2,4 & 8 amp rate. My truck had the original Delco Agm. I bought a new battery for the truck and put the batteryminder on the old battery for 3 months. No change in battery's condition.
On other batteries, it may take weeks or a few days to run through the complete cycle, but when it's done, the charger goes in to a default, gel and 2 amp light flash.
I do have a mower battery made on 2008. It's rated at 340 cca. My battery conductive tester shows it's bad. Battery makes 240 cca. My batteryminder has spend a lot of time on this battery the past winter with no noticeable change in the cca.
However, you can buy a new cheapie mower battery rated at 200 cca. So I've learned to buy the bigger battery and even though it's shows bad, it can still out preform a new battery. I will install the 2008 battery in a mower that is close to home, so I can keep an eye on it.
My farmall, IH C, has a very old 12v battery, can't say just how old, but old. It has one cell that is weak, battery conductive testor shows battery is bad. However when you hit a 6v starter with a sick 12v battery, the starter flips the engine over like it's a healthy battery. Had I not used a hydrometer or the battery conductive testor, I would think the batteryminder was doing GREAT. I just moved the batteryminder to the IH C this morning.
The way I feel about the batteryminder it won't reverse the aging process of a battery, but hopefully it will slow down the aging process.
I have a very old 12v battery on the Jubilee too. Same as the IH C. An old wimpy 12v can move a 6v starter faster than a good 6v battery.
You slow down the aging process of a battery by keeping it fully charged even if you use a trickle charger. Just don't over charge it or you will damage it.
Just my $.02 worth.
I won't spend $100 on another batteryminder.
I like my battery conductive tester. It lets you know your battery is about to take a dump, so you can do something before you get stranded.