Connecting Multiple Batteries

[gtippett]

Hello Everyone,

Just a question that is always in the back of my head when I put the batteries back into the RV after winter. Is there any items that I have to be careful of? I understand that the red (positive) cables are connected first, then the black (negative). However, sequence wise, do I connect all the batteries together first (both red and black), then connect the battery bank to the RV... or do I do all reds (batteries and rv) then all the blacks?

Also, I will have the entire RV shutoff with switches that I have installed, so there will be no loads (all red wires goes thru a switch prior to connecting to the components). Should I be concerned of sparks? Do I need to ensure the cables don't touch anything metal while I am connecting the cables?

Thanks in advance for the insight. This is the first year that I will be reconnecting multiple batteries to the RV along with a solar system and inverter.

[AlexPeterson]

The reason that all the positives should all be connected prior to any negative terminals is so that you can tighten all the positives without worrying about creating a short, should the wrench hit some part of the chassis while tightening a positive terminal. Be sure all the positives are covered/guarded before connecting the negatives.

Make sure the solar charger is off or disconnected until the batteries are connected.

[howson]

gtippett -- are your batteries in parallel (12v batteries) or are they in series (2 ea 6v batteries)?

Cate&Rob has a lot of experience with this, though on a boat, so I expect he'll chime in soon.

Howard

[gtippett]

howson, they are in Parallel, two 12 volts.

[Country Campers]

Also make sure batteries are fully charged before paralleling them, I am not sure why though just what I have learned.

Brian

[TucsonJim]

Also make sure batteries are fully charged before paralleling them, I am not sure why though just what I have learned.

Brian

Brian - If one battery is partially discharged, it will be seen by the other battery as a drain, and if the voltage potentials are significantly different, it would be similar to hitting the good battery with a short circuit.

Jim

[howson]

howson, they are in Parallel, two 12 volts.

Then AlexPeterson's and Country Campers' inputs covered it (to the best of my knowledge).

[Cate&Rob]

All good advice. The only thing I would add is to load test each battery before they are connected together. The biggest problem with a parallel battery system (unless you have a swiitch for each battery) is that a weak battery will discharge a good battery or cause the good battery to be overcharged.

Rob

[Scott'n'Wendy]

Negative to rv last as Alex said. When doing battery banks, I always wrap the handles of my tools with electrical tape to guard against shorting any batteries.

[gtippett]

Thanks Everyone for the responses. I have a Victron battery charger that I use on them while they are at my home. They are lithium's and they don't need much attention over the winter. As for the connections, I will do all the positives first then the negatives. So last question... with the loads off, as in the systems are isolated from the batteries by switches, I should not see a spark when connecting the negative cables, correct? As they won't be a sudden draw of power from the battery, right?

[howson]

Thanks Everyone for the responses. I have a Victron battery charger that I use on them while they are at my home. They are lithium's and they don't need much attention over the winter. As for the connections, I will do all the positives first then the negatives. So last question... with the loads off, as in the systems are isolated from the batteries by switches, I should not see a spark when connecting the negative cables, correct? As they won't be a sudden draw of power from the battery, right?

If the RV has a "true" battery disconnect (that you or someone else added) then it's unlikely there will be a spark. The OEM "battery disconnect", as you probably know, isn't a complete disconnect therefore a small spark may be witnessed (but still unlikely IMO).

[gtippett]

If the RV has a "true" battery disconnect (that you or someone else added) then it's unlikely there will be a spark. The OEM "battery disconnect", as you probably know, isn't a complete disconnect therefore a small spark may be witnessed (but still unlikely IMO).

Yup I understand the limitations of the OEM disconnect. Prior to reconnecting the batteries, I am installing the missing disconnects, one for the bus bar (power to the RV) and one for the inverter. I already have a disconnect for the solar panel installed.

[Country Campers]

I think you will be in good shape then. Connect batteries and then turn on the power and away you go.

Brian

[AlexPeterson]

gtippett You might still see some sparking when hooking up the negative on the second (and more) batteries if the states of charge are slightly different. Juice from the higher state of charge battery might move towards the lower state battery. Should not be a big deal unless they are way out of balance.

[Lonestar]

Is load testing (the type they usually do at automotive stores) really a good idea on deep cycle lead acid batteries? As opposed to automotive batteries where a large current surge is needed to provide starting capabilities, RV batteries just need to provide a stream of relatively low current.

Wouldn't it be less harsh or damaging to charge the RV battery and then after a resting period check the voltage or specific gravity of the acid?