- Joined
- Dec 7, 2020
- Posts
- 6,934
- Reaction score
- 17,578
- Location
- Minneapolis, MN
- Ram Year
- 2017 2500 Laramie Crew Cab
- Engine
- 6.4L HEMI
This is the heart of every modification; I'm going to spend money on upgrades to make it better. Sometimes this works, sometimes it doesn't.
Imagine spending just $180 on an Interstate 27F. That battery is lead acid and has a reserve capacity of 165 minutes (25 amp load until 10.5V). Compare that to an Optimal Yellow Top. 140 minutes reserve capacity and $380. While the Yellow top may advertise 830CCA vs the Interstate 710CCA, the Interstate has more reserve. Both ratings assume battery is fully charged, a situation that won't happen with the Optima if you charge directly from the alternator. I've gone through probably a dozen AGMs in search of something 'better'. Those batts, while always starting the vehicle performed worse in a camp environment where there was continuous draw (i.e. fridge, lights, etc) than lead acid. Once I figured out that you need something like a RedArc BCDC 25 to correctly charge an AGM things started working.
So your $380 Optima is only really getting maybe 80-90% full and is never achieving it's advertised performance. You feel better because you've 'upgraded' and because you have no direct measurement of state of charge you assume it's bringing value. But in reality it's not.
If you want to run electronics longer, you need a bigger battery (or a second battery) not an AGM. Lithium is a much better choice for extended run time (you can take those down to almost full depletion), but I wouldn't recommend that for under the hood, nor for starting loads. I'd run an AGM in something like a desert racer where it is exposed to extreme vibration, but not in a daily or camp rig.
A couple of good resources to consider:
https://workshoppist.com/car-alternator-charge-agm-battery/
https://www.interstatebatteries.com/blog/how-to-charge-an-agm-battery
Look at Amp-hours.