You need something other that the oem indicator as they are horrible. Mine says batteries are "good" at a 50% SOC which is a bit below good.

The trimetrix is good, but from what I hear the amp hours in/out isn't real accurate. A simple voltmeter can tell you just as much, or more. If you want to know more get a ammeter too.

 

Mine seems to be quite accurate, but you have to be careful to use twisted pair for the sensor wires, avoid running them along current carrying cables, and don't use the sensor wire to also provide negative to power the gauge. It is only reading a fraction of a milivolt when the is less than an amp charge or discharge.

I did, however, have to adjust the battery efficiency setting on the meter slightly to get it to show 100%.

 

I have sold a lot of batteries in my lifetime. And this is the only way to go. I had to use an inverter to run medical equipment all night and never a problem. It is more money but way worth the extra cost. these batteries are made to sit with non use for a few months. That added I would not put a tender on them as they are made to be discharged way DOWN, THEN RECHARGED. as he said CCA means nothing it is reserve capacity. That is how long the batter will last at a certain draw. You could have 1000 CCA if you can only use that for 10 seconds then it is no good. But the batters can be sold as 1000 CCA.
and that is not what you want. I hope it makes since to you all.

 

Dave I don't want to pop your bubble. there aren't many battery manufacturers. And they are made to the disturbers specs. I have sold them all. Caterpillar, John Deere, Prestolite. They came from the same truck. the only way you might be able to tell is by weighing then a good battery had more lead. adding to Reserve Capacity. All three of those brands were made or came from the same manufacturer. If you want to test the theory out start picking up the cheaper batteries and look at the CCA. most likely there will be very little difference in the CCA but if they will have Reserve Capacity you will see a big difference. I sold parts for well over 40 yrs. and went to a few classes. Some warranties are geared around you selling your car before the battery goes bad. Don't you ever wonder why so many OEM Batteries last longer that replacements battery's I think this answers what these people are thinking. Oh and Ive been to a few classes on this subject plus many batteries people consider bad are not bad. I made a lot of friends by recharging a battery then testing it. You can not test a discharged battery.