Battery charge question

[bridma]

I have 2 batteries, a start and a deep cycle house. I have just put a portable trickle charger on one of the batteries (the battery selection switch is in the "off" position), and plan to trickle charge the other battery tomorrow. In future, can I put the selector switch on "both" and will both batteries charge up together? At present I do not have battery guages.

Martin.

[thataway]

I would charge one battery at a time. I would not leave a trickle charger on the batteries, since they tend to often be poorly regulated, and can lead to loss of electrolyte and sulfating.

[journey on]

Lead acid batteries vary in at-rest and discharge voltage levels by small amounts.. If 2 lead acid batteries are connected in parallel and just allowed to stand, the small difference in their voltage will discharge one "into" the other and eventually you'll have 2 flat batteries. So, you can't just turn the battery switch to both and walk away.

Now, if you're charging them,things are different. Both batteries will be above their rest voltage by the amount determined by the battery charger current/voltage control. Thus, neither battery will discharge into the other, but will accept charge current from the charger. So as long as the battery charger maintains a decent charge voltage (~13.0 to 14.2 volts) you can charge them in parallel. And you can check this voltage easily with a volt meter.

If the charge voltage is less than 13 VDC after the batteries have been on charge for a while, the trickle charger doesn't have the current capacity to maintain both batteries and you'll have to charge them one at a time. As I mentioned above, if the charge voltage climbs up above 13 VDC, your charger is good for both.

As Bob said, if the voltage goes above ~ 14.7 volts, the battery charger isn't regulating well. But that would be true of both one battery alone or 2 batteries in parallel.

Boris

[Robert H. Wilkinson]

Hi Martin, both Bob and Boris are knowledgable and give good advise regarding batteries.

Trickle chargers vary greatly and like Bob said some are not regulated with any degree of accuracy. A fully charged battery - at rest and with any surface charge drawn off should be 12.6v. A quality charger should hold a float charge of around 13.6v. The key is to maintain a battery between these 2 voltages. Below 12.6 for any length of time and it will start to suffer, above 13.6 for too long (after it is charged) and it will start to loose electrolyte.

It is not neccesary to leave batteries on a maintainer 24/7 all winter. I recommend plugging your trickle charger into a timer and set it to come on maybe 1 hour every 24. The "on" time would depend on what voltage the charger raises the battery to. I leave mine hooked up to the onboard (15amp) charger so 1 hour is plenty.The small 1 or 2 amp maintainers can be found fairly cheap, and could be left on longer. I would recommend 1 on each battery - they can both be plugged into the same timer - leave your battery switch off. This is assuming that your batteries are fully charged to start.

Voltage and electrolyte level should be checked at least monthly. Unless your maintainer uses pulse technology I would recommend giving your batteries an equalizing charge( at a higher voltage) in the spring.

Regards, Rob

[joefish]

Hate to chime in with a firecracker question when you guys seem able to construct the atom bomb but I'll do so anyway.

I have a start battery and two house batteries. Before I leave for the Keys in a couple weeks I'd like to have everything charged and ready. Can I keep the
battery selector switch turned to "off", hook up a regular (not a trickle) battery charger to the starter battery and charge - without unhooking the cables from the battery? Or is unhooking the cables from the battery being charged important? I may sound lazy, as well as uninformed, but it's been darn cold and those batteries aren't all that easy to get at. Thanks!

[Robert H. Wilkinson]

Hi Joe, there is no need to unhook battery cables. Essentially the battery switch does that for you. Hook your charger up to the common or since the back of the switch might be hard to get at - the cables that go to the engine. This is where an installed on board 2 bank charger comes in handy! Set your switch to #1 and it will charge your start battery. After it is sufficiently charged select position #2 and it will charge your house batteries. Since you have 2 house batteries, this may take longer.

Not a rocket scientist here Joe just glad if I can help somebody once in a while. C Bratts has so many knowledgable contributors though - you have to be quick on the keyboard! Never seen a boat owners forum with so many people eager to help and talk about boats.

Regards, Rob

[journey on]

You're darn right it's cold outside, got down to 41 last night. Anyway, here's my take on your question. And I'm providing you with all this BS so you can have some idea as to what needs to be done and time your ventures outside accordingly. Sorry if it's overkill, but I have a lot of time on my hands right now.

First, you're right, lead acid batteries aren't rocket science, they don't fly on rockets. And what they fly now is certainly beyond me. However, here on earth we all have to deal with lead acid. Charging is entirely different and more complicated. So here's my advice.

If you have an "old" charger, they consist of a transformer and a diode bridge which charges the battery in a series of pulses with no more control that the transformer setup. The charger I bought in the '60s recently died and I got a "modern" charger (cheap, Chinese) which charges in 3 steps: 1. Current limited to pack as much amp-hrs in as possible quickly, 2. Voltage limited, to not overheat the battery, and finally 3. a lower voltage to provide a float charge to maintain the battery. And it takes a long time to charge a lead acid battery, so step 3 is reached in about 24 hrs. Actually, I think that even the float charger I got from Harbour Freight has those capabilities.

So, lets assume you have a recent "modern" charger. So anywhere in the wires leading to the battery you can connect the charger appropriately. Wherever is easiest: at the battery, at the battery switch, at the motor leads, even at the instrument panel. I connect Journey On's battery charger at the batteries, since that's the shortest route. For the battery switch, motor leads, etc. the battery switch has to be on, right? Every day or so check the battery voltage to make sure it's not out of whack, and also remember to check the battery water. Overvoltage will eventually boil the batteries dry but that's a matter of days, but lack of water is guaranteed to kill a battery quickly. When you see how everything is going, you'll know how long between checks. Should be on the order of a week or so, and then maybe forever. Pray for warm weather whilst you're doing the setup, but just remember Feb should be colder than Jan, so learn early.

I installed a 3 bank battery charger in Journey On so each bank (2 ea) is wired to a different charger output. But I can't see any problems with charging 2 batteries in parallel AS LONG AS the battery charger can handle the current.

So find out if you have a decent 3 stage charger, hook it on and check it for a while then let it rip.

Boris

[bridma]

Again you guys came through. What a great bunch you are. The information and help on this forum is second to none.

Martin.