Maintaining Two Batteries With One Maintainer....

[Utopia Texas]

If two 12v automotive batteries are connected together with a battery switch will a maintainer on one take care of both batteries at the same time? Will a small 2 amp maintainer unit keep up two batteries if they are in good shape or should a larger amperage unit be used? thanks...

 

[davesl708]

If the switch keeps both batteries connected they will act as one battery. The two amp should maintain them if they are in good shape.

 

[Utopia Texas]

Any recommendations as to "Brand"?
There appears to be dozens of units on the Internet at really varied prices.....

 

[Industrial Toys]

These units tend to send high frequency pulses to the batteries to break loose the sulphation. I have a friend that has six or so batteries connected at once to one small unit. I find this obsession with your batteries a bit over the top, myself. Better have fuses on each line though as batteries have a lot of stored energy!

Some are very expensive and some from China (on E-Bay) are very cheap. I suspect that certain cheap ones are as good as the domestic high cost ones. I was looking into getting one, but got side tracked.

So unfortunately, I can't reccommend which cheap ones to buy. I would probably go with a cheaper one that has some technical information, not just claims like " batary lasting very long time" or "make stronger start". You get the idea.

 

[the old grind]

Wire diodes in a way that current can't flow any way but toward each battery from the charger. (Remember those isolator kits for cars trucks that had 3 posts on a large heat sink? Same deal, and you don't want a circulating current loop between the batts.) Whichever one can use the charge will take it, but they won't be going back & forth between each other this way. (not so good for them)

You can set up a bench charger with a diode on each + of several take-offs or clip sets. They will divide the current according to their state of charge. Chargers' no load vs loaded voltages will vary, so be less concerned with voltage when charging. After any charging cycle give the batteries a 1/2 - 1hr rest before checking voltage. 12.7v NL means they're in good shape.

btw, Just prepped a 'dry-charged' batt for boss' quad. Instructions said to wait 1/2 hr after adding acid before charging and to charge at 2A with a floating circuit charger (14 A/Hr batt, btw) then rest another hour before use. The battery will still work if you rush thru this, but useful life will be shorter. (BTDT with puny 16 A/Hr batts in 'big twin' motorbikes w/o kick start & lucky to ever get two seasons out of one. AGM batts are better when sized small for load and are shipped 'wet')

It's a good idea to trickle any unused battery as all lead-acid types will self-discharge over time, and being on concrete can't be blamed anymore (old myths die hard), nor can greasing/sealing terminals prevent it. I built a YouTuber light bulb 'regenerator/desulfator' (high V, low A pulses, w/1A fuse) and have had good success recovering batts that have no cells shorted internally. No-load voltage reads high on meter's DC scale, but falls right into the mid-13s - 14v when connected.

Battery life is inversely proportional to time spent at full charge, the reason your daily driver's battery lasts so long. Topping up is as important a routine as checking tire pressures, lug nuts/bolts or loader bolts but doesn't ever have to be as much work. tog

 

[Industrial Toys]

A diode junction will give you a .6 volt drop! Not sure if that would matter with HF pulses though, but if it is also a charger, you would loose .6 Volts.

I can't understand why my GMC gauge seems to show 16 or so volts and doesn't boil my batteries dry with it's HD alternator, in no time at all?

 

[3930dave]

Of the latest types, I have the Ctek 3300.

Battery Chargers - CTEK Battery Chargers

It is more money than some of the basic ones. Why it's worth more money to me:

1) Puts out 3.3amps max. Decent capacity vs. compact case size. Easy to tuck into smaller spaces.

2) Does have de-sulphation mode.

3) The unit is well sealed against water and dust (IP rated). I can use it outside in less than ideal weather.

4) It has a cold weather/AGM mode. Standard flooded lead-acid batteries benefit from a higher charge voltage in cold weather. AGMs like a higher charge voltage in general.

I'd stay away from the $8 tenders - a few folks have cooked batteries on the stuff Industrial is warning about. Battery Tender seems to be popular, but it's one I haven't tried.

Automotive

Around here I can find CTek or Bosch equivalents for less money than Battery Tender.

Rgds, D.

 

[AaronS]

I have 2 outboard deep-well batteries that I use for the trolling motor on my boat, that are connected in series. I left them connected in series when I removed them from the boat for winter storage, and connected my Battery Tender Junior. It has done a great job of keeping both fully charged.

 

[3930dave]

I have 2 outboard deep-well batteries that I use for the trolling motor on my boat, that are connected in series. I left them connected in series when I removed them from the boat for winter storage, and connected my Battery Tender Junior. It has done a great job of keeping both fully charged.

Are those 6 volt batteries, or do you have a 24 volt charger Aaron ?

Rgds, D.

 

[AaronS]

Are those 6 volt batteries, or do you have a 24 volt charger Aaron ?

Rgds, D.

I apologize, I meant connected in parallel, not series! 12 volt batteries with a 12 volt charger.

 

[davesl708]

I use a Minn Kota charger/maintainer on my boat. Keeps two deep cycle and one starter battery in great shape. Bats stay on the boat year round and have been getting 8yrs out of the batteries. The charger is 10yrs old now.

 

[Trillium Farm]

Of the latest types, I have the Ctek 3300.

Battery Chargers - CTEK Battery Chargers

It is more money than some of the basic ones. Why it's worth more money to me:

1) Puts out 3.3amps max. Decent capacity vs. compact case size. Easy to tuck into smaller spaces.

2) Does have de-sulphation mode.

3) The unit is well sealed against water and dust (IP rated). I can use it outside in less than ideal weather.

4) It has a cold weather/AGM mode. Standard flooded lead-acid batteries benefit from a higher charge voltage in cold weather. AGMs like a higher charge voltage in general.

I'd stay away from the $8 tenders - a few folks have cooked batteries on the stuff Industrial is warning about. Battery Tender seems to be popular, but it's one I haven't tried.

Automotive

Around here I can find CTek or Bosch equivalents for less money than Battery Tender.

Rgds, D.

That's what I have and wouldn't use anything else !!!! Especially if you have a modern battery.

 

[3930dave]

I apologize, I meant connected in parallel, not series! 12 volt batteries with a 12 volt charger.

No Worries , as long as nothing was wired up as 24v.

Rgds, D.