How low should I take my voltage?

HappyCamper2024 · November 16

Hi there. I'm a new owner of a 2023 signature series 320s. First owner. Like many people it seems my victron controller thinks I'm on a default AGM battery but the camper came with a deep cycle marine SRM-24 battery.

During the walk through the service guy told me I can just run the battery all the way down and recharge it, no problem. I'm not sure that's true. Per the controller is gets to 14.27V when the sun has charged it and it's just sitting but the daily draw takes it down to the 12.60's as a low.

The Victron history shows it was at 3.77v for a few days before we picked it up, but I haven't gotten it under 12.40v in my driveway, just playing music, charging stuff, using the overhead fan.

So, if I'm out boondocking, trying to keep it lite, how low can I take that voltage on the battery? I tried googling it generally but didn't get a clear answer.

I'm a total newbie so assume I know very little. Thanks, y'all.

Thank you.

MuttonChops · November 16

First off, please confirm you have a Standard Lead-Acid (AGM or not) Battery [dealer installed] or the yr-2023 factory installed OPTIONAL Li-ion package.

Lead-Acid and Li-Ion have very different useful voltage/charge output profiles.

Generally, Lead-Acid Batteries are only usable for half their rated Amp Hours capacity.
For example; 70AHr Deep Cycle will become useless after 35AHr of energy is drawn out and the 'measured' voltage will be in 11'ish to 12.2'ish range.

A 70AHr Li-Ion battery would still generate 12.5+ volts after 60AHr of energy drain.
The 'serivce guy' may have assumed the trailer was Li-Ion.

Best Practice is never to fully drain any battery below 12.2'ish volts

When Shore-power is available (like in your driveway) use it.
You can enjoy the trailer and battery will be charged and ready for your next trip.

Marceline · November 16

Is it this battery?
https://www.interstatebatteries.com/products/srm-24

If so, I wouldn’t let it go below 12.1v

HappyCamper2024 · November 16

We definitely don't have the lithium battery, just a Deep Cycle Marine Battery. The "default" in the settings is a Gel Victron Deep Discharge. The dealer did not tell me about the Victron. Said there was no way to tell how much battery is left, just use it and recharge it if it runs out. Thank goodness I've been lurking here!

The solar power faces morning sunshine and it seems to spend at least a third of the day on float. I haven't plugged it in yet because I'm trying to get a sense of how quickly the power draws down doing minimal activities. Apparently the answer is Very Quickly.

Thanks for the info. I might switch over to an AGM or even the one the default is set on. It looks like it's as easy as turning the disconnect knob and unhooking/rehooking.

pthomas745 · November 17

I'm a bit surprised that your camper came with a "stock" lead acid battery. If there is any question, have a look, take a picture, and we can help.

Your dealer doesn't know "anything" about batteries if that is the answer he gave you.

The balancing act on any battery type is "how much power to use to get the most cycles from the battery". The kicker for a battery is: no matter how well you treat it, the "calendar aging" of the battery is unavoidable. Even if you never dropped a lead acid battery to the 70-80 percent range shown in the chart above...it still will not be a viable battery after 5-6 years. So: to get the most out of the battery, use the power you need, try to avoid going too far below that "50 percent" level. If you do, get the charge level back up as quickly as you can.

The absolutely fastest way to kill a battery is to leave it in a low state of charge for a long period of time. Even a 1 year old battery left in a low state that continues to "self-discharge" will completely "sulfate" and fail.

So, that is the dilemma: to get the most out of your battery...you should use the available amp hours, within reason, of course. This may take a bit of planning if boondocking to balance your usage with what you might expect for solar input, etc. Monitoring the battery is really the key to get those 5 years you might expect from a lead acid battery.

Victron has some very odd names for what they call ordinary deep cycle lead acid batteries. Most of those settings that Victron has for lead acid charging are very much the same, so I wouldn't worry about them too much.

AnOldUR · November 17

Using the number of charge cycles to rate a battery is misleading. You don't age a vehicles by how many times you filled the gas tank. You do it by total miles driven. Running your tank dry may suck crud from the bottom of the tank and cause damage, but over the life of the vehicle, filling at a quarter tank instead of half will get you the same distance from the same amount of gas, regardless of the number of times you went to the gas station.

All this to say that from what I've read, you can take an AGM battery down to about 20% without changing the total amps you'll get from it over the life of the battery.

I made that way to complicated, didn't I?

Marceline · November 17

HappyCamper2024 said:

We definitely don't have the lithium battery, just a Deep Cycle Marine Battery. The "default" in the settings is a Gel Victron Deep Discharge. The dealer did not tell me about the Victron. Said there was no way to tell how much battery is left, just use it and recharge it if it runs out. Thank goodness I've been lurking here!

The solar power faces morning sunshine and it seems to spend at least a third of the day on float. I haven't plugged it in yet because I'm trying to get a sense of how quickly the power draws down doing minimal activities. Apparently the answer is Very Quickly.

Thanks for the info. I might switch over to an AGM or even the one the default is set on. It looks like it's as easy as turning the disconnect knob and unhooking/rehooking.

I would correct the Victron settings so the controller is set up for your battery. Victron has all the manuals at its website. I wouldn’t let the voltage go below 12.1v. If you plan to do a lot of boondocking I’d consider adding a Victron SmartShunt so you can more accurately measure power use. That battery is also inadequate for any real boondocking.

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