Battery choices again

[alanmalk]

Originally Posted by Bobbie54

One is fully charged. So I'd have to charge the other before connecting. I've considered just connecting to one with a switch to switch to the second if the first got low- sort of like the gas tanks- but not sure there would be any advantage (unless there is a lot of current between them.)

But question on that. Say I charge both, hook up, and there is a current. Doesn't that just level them to the same charge? Slight loss of heat to resistance but other than that should conserve the available energy.

The "A-B-Both" switch is used to switch between 2 batteries or to put them in parallel when heavy drain current is expected. Its a conservative approach to saving one battery for emergencies, commonly in situations where loss of both batteries has severe consequences - like on the open ocean. It would also work to prevent one battery from draining the other but puts the burden of keeping track of which battery is in use and switching - on to you.

Would they level out? To a certain degree they will, especially if the same age & condition & manufacture. But the current will never go to 0 due to the fact that batteries self-discharge. A perfect match in both charging and discharging states is very unlikely. So measure the current after a day or 3 and decide if it within your tolerance and recharge ability. Mine stabilized to around 5 ma in about a week - but they are matched AGM batteries. I probably should check again now that it has been 5 years since I checked last.

Heating loss in a few inches of battery cable at the milli-amp level is trivial.

--
Alan

[Bobbie54]

I get that but if one battery is sending current to the other isn't that also recharging the second one? Where is power actually lost?

[alanmalk]

Originally Posted by Bobbie54

I get that but if one battery is sending current to the other isn't that also recharging the second one? Where is power actually lost?

It is not recharging the second one. It is compensating for the self-discharge. The battery with the higher voltage (the "charger") is the one that is losing the power. The other stays the same - does not gain anything. Result - a net loss. Maybe trivial, maybe significant. You don't really know for sure until you measure it.
--
Alan

[Brian B-P]

Originally Posted by Bobbie54

I get that but if one battery is sending current to the other isn't that also recharging the second one? Where is power actually lost?

If there's a large voltage difference, then yes the more charged battery will charge the less-charged one. The energy which is lost is lost as heat due to resistance, mostly internally in both batteries.

[John in Santa Cruz]

my issue with dual 12V on an A/B switch is charging, the disconnected battery probably isn't getting charged unless you have 2 seperate chargers, one for each battery.

[Brian B-P]

Originally Posted by John in Santa Cruz

my issue with dual 12V on an A/B switch is charging, the disconnected battery probably isn't getting charged unless you have 2 seperate chargers, one for each battery.

That's a reason to use a switch with A / B / A+B / Off positions as Alan mentioned... and charge on "A+B". While both batteries are connected to the charger, and the charger is on, the batteries both charge (at possibly different rates depending on their state of charge and internal resistance).

This is an example of a suitable switch (the model which Ron in BC uses):
m-Series Mini Selector Battery Switch
This is an equivalent from Marinco:
Panel-Mounted Battery Mini Selector Switch

[Bobbie54]

I think I'll just get another 12V and have them both connected. This one isn't very old so should still be pretty good compared to a new one. And I have the battery box since that's how the trailer used to be set up. But it is nice to have options!

[alanmalk]

Originally Posted by Bobbie54

I think I'll just get another 12V and have them both connected. This one isn't very old so should still be pretty good compared to a new one. And I have the battery box since that's how the trailer used to be set up. But it is nice to have options!

Quite reasonable plan and the least expensive as you mention. But arrange for a small charge on a regular, if not continuous, basis - to offset any losses that may be happening. A worse case scenario is that the slight mismatch could discharge both batteries quicker than you might expect. When not using the trailer a 10 watt solar panel with no controller or 1 Amp trickle charger will do the trick.

--
Alan

[Seneca]

This is a very helpful thread. When I was ordering my new Escape 19 I was completely unsure of what path I wanted to go down in terms of electric power supply--solar, generator, enhanced battery capacity--and got some very good advice to the effect that people have strong opinions, but until you've used your unit for a season, you really don't know what you want, so go with the basic system and see how you feel after a season of camping.

After a season, I still feel like I can put off solar or a generator, but am coming around to the conclusion that a little more battery would be nice. This thread points a way to doing that without junking a nearly new (six month old) 12v battery with just one season of use on it. And I'm cheap enough not to want to do that.

Thanks.

[Bobbie54]

I keep it plugged in in the garage so what I'll do when I get the new battery (soon) is disconnect the first, charge up the second, them connect them up together.

[dstreight]

The other salient benefit to 2 6v FLA batteries in series...per Trojan, you can safely discharge to 80%.

It would be useful to have a current measuring shunt apart of your battery array...to more accurately know its state of charge...

[dstreight]

Originally Posted by Bobbie54

I keep it plugged in in the garage so what I'll do when I get the new battery (soon) is disconnect the first, charge up the second, them connect them up together.

What charger are you using?

[Bobbie54]

Originally Posted by dstreight

What charger are you using?

I just plug the trailer into house current (with an adapter). So if I wanted to charge only one battery I'd disconnect them (but what I'll probably do is disconnect battery 1, charge the new one, then reconnect in parallel).

[dstreight]

Originally Posted by Bobbie54

I just plug the trailer into house current (with an adapter). So if I wanted to charge only one battery I'd disconnect them (but what I'll probably do is disconnect battery 1, charge the new one, then reconnect in parallel).

I'm not familiar with what Escape uses for charging via shore connection. Is it smart charging with sensing profile(s)?

[Brian B-P]

Originally Posted by dstreight

The other salient benefit to 2 6v FLA batteries in series...per Trojan, you can safely discharge to 80%.

That's true of any battery of any voltage in that product range; for instance, in Trojan's Signature Line there are 6-volt, 8-volt, and 12-volt models, all rated to the same 750 cycles at 80% DOD or 1200 cycles at 50% DOD. Very few people using 12 volt batteries use the same grade of battery as they would if buying a 6 volt battery, but they're available.

[Brian B-P]

Originally Posted by dstreight

I'm not familiar with what Escape uses for charging via shore connection. Is it smart charging with sensing profile(s)?

The WFCO 8955 power centre includes a typical multi-stage "smart" converter/charger (max output 55 amps). How "smart", and whether the logic and voltage levels are appropriate, are subjects of much discussion; it doesn't sense anything other than its own output voltage and current.

[Meandering Minstrel]

That's a really good summary of batteries and battery life. Thanks

[j3cub]

Bobbie54, I added a second 12v batt to my trailer and had no problems. I did wire them in parallel + to +, - to - but then when I hooked up to trailer I hooked - to one battery and + to the other battery. This way it made sure both batteries were being utilized equally. Also tons of fun camping with you and Mimie in Washington! PS, 6 volt batteries are so dam heavy.

[Brian B-P]

Originally Posted by j3cub

PS, 6 volt batteries are so dam heavy.

The weight of a battery is unrelated to the voltage. A 6V battery and 12V battery with the same energy storage capacity (e.g. 200 amp-hours at 6 volts or 100 amp-hours at 12 volts) and of the same construction (e.g. heavy-duty deep cycle) are the same weight and volume. Yes, you can buy 12V batteries which are smaller (and therefore lighter) than the most common 6V size (which is the GC2 commonly used in golf carts), but they come in lots of sizes.

Boxes of lead, whatever the voltage, are heavy.

[cpaharley2008]

I believe the lead plates in the 6 volt battery are thicker, thus heavier.