Mea Culpa: my own battery charging

I grouse enough about the mistakes others make;  here’s how I am undercharging my own batteries and doing some amount of damage.

My campsite is in the Mount Hood national forest.  Tall conifers of some kind make solar charging problematic, even with a 2.6:1 overpaneled system.   I moved spots a few times to maximize the amount of sun I can catch.

Normal situation:

  1.  run the bank down to ~12.4v-12.5v overnight

  2. hit Vabs after 10am and finish Absorption some time after noon.

Reminder that my batteries are fully charged when current acceptance (endAmps) at Vabs has fallen to C/125, or about 1.75A.

Getting insufficient charge means my voltage will be a bit lower in the AM, making the next day’s charging even tougher.  It’s also been chilly so I’ve been running the heating pad for dog and I.

  1. 12.3v this morning

  2. Right now it is 1115 and the panels are putting ~245w net into the battery bank (gross 370w but there are loads like fridge, roof vent, etc).  Voltage is my bank is 14v.

  3. the controller has been maxxing out on absorption duration (180mins) with current acceptance still around 4.5A. The bank is not getting fully charged, a cardinal sin for a lead-charging nazi like me.

There are ways to get around the absorption timeout, but none of them work in this scenario since I am simply out of sun.


  1. spin the alternator for a while in the morning.  Optimal use might be to do it right before the sun breaks though the trees, so solar can take it directly from there.  I am loathe to do this for purist reasons, and wear/tear on the vehicle reasons.

  2. move to another campsite with better view of the sun.  That’s the long-term plan, but I’m not ready to move yet.

  3. rewire the panels serially to allow for better production in partial shade - been meaning to do this but I don’t presently have a ladder.  I want to do this when encamped in one place with stable weather conditions.

  4. reduce overnight loads - this means break out the sleeping bag instead of using the heating pad.  I’ve been lazy.

  5. reduce power consumption during bulk and early absorption to give the system a chance.    That’s what I’ve done this morning.  I hit Vabs at 1135 (a few mins ago)   Acceptance has begun to fall and there are presently 227W going into the battery instead of 245w.  When it drops to 150w I will run some other loads I have in mind, since there will be ~100w of untapped power available then.

I think if I can get one full charge I’ll be “over the hump” and it will be easier to get and stay charged in this campsite.

The 180min Absorption timer on my controller will trip at 1435.  If it’s not down to 1.75A by then I should have enough sun-time to restart the Absorption and finish.

Update:  couldn’t get it done.  Absorption timed out with 3.76A still being accepted.  Within 10 minutes of that (before I could restart Absorption) the sun started going behind the tall trees.

Updated again later that evening.

  1.  I moved to another site in the same basic area where I think I’ll get more sun.  In the morning it will get sun somewhat earlier then in the afternoon it will get sun much later.

  2. I watered the batteries, then cranked up Vfloat == Vabs == 14.7v (east penn specifies 14.4v - 14.7v for this battery, toward the higher end for cycling)  This is an attempt to get around the 180min max duration of my controller, and isn’t unusual for solar-only charging deeply-cycled batteries off grid.

  3. If that gets me to a stable endAmps (1.75A/25w) going into the battery without  too much extra time at that voltage I’ll keep it there and just water more frequently – east penn allows up to 12 hours of Absorption, and there’s no where in CONUS where I could hold Vabs for that long.    If I get to endAmps with hours of sun left in the day I’ll start dropping Vfloat into a high float (east penn says 13.8v - 14.1v, so I might try 14.1v).