Constant trickle charge vs. periodic top-off charge

[richard5933]

We've got three 8D batteries on our 4108 at the moment. Two of them supply power to the 24v coach system, and the third is the generator start battery. (I know that the 8D is overkill for the generator start battery - topic for another time.) There are no house batteries on the coach at this time.

At the moment, I've got all three 8D batteries in place in the coach but disconnected. I am going out every week or two to top off the batteries using a 12v three-stage automatic charger with a max output of 15 amps. I hook it up to each of the three batteries separately until each is fully charged. The batteries are typically down 10-15% from full when I first connect the charger and let it take a reading. Temp outside today is hovering around 0F and was about -10F last night. Today they were at 80% of charge when connecting, based on the charger's on-board reading.

There are on-board chargers on the coach which I could just leave plugged in, but they are from 1974 and I suspect would end up just boiling the batteries. Until I can update the chargers in the coach, I'm going to keep them charged with something safer than the old units.

Question is this...

Is my current routine of periodic topping off the charge on the batteries every week or two likely to successfully take me through the rest of the winter? The alternative I see is to purchase a couple of trickle chargers and leave them plugged in, but I'm not really sure that it would end up with any better results.

Not being a battery engineer, I don't know if the batteries will do better being at a constant 100% or if the fluctuation with the periodic top-offs is also okay.

Any battery gurus out there with advice?

[Iceni John]

Why are the batteries losing so much power over such a short time if they're disconnected?   Do you still have some phantom loads connected, even though they are turned off?   Are they old or sulfated?   Flooded lead-acid batteries should self-discharge no more than about 5% per month, with less in cold weather and more in hot.

Ideally a small constant trickle charger is better than intermittent charging, but as long as the batteries are not more than a few percent down I don't think it really matters.   If you decide to trickle-charge the batteries, you may however wish to use a separate charger (usually sold as 'battery maintainers') for each battery, so if one battery needs more charging than another you won't risk overcharging or undercharging them.   I've recently bought two small Steca Solsum 6.6 solar charge controllers for my two start batteries, specifically because the battery that's permanently connected to the engine's DDEC computer needs slightly more charging than the other, even though the DDEC draws only about 8mA when asleep.

John

[richard5933]

Why are the batteries losing so much power over such a short time if they're disconnected?   Do you still have some phantom loads connected, even though they are turned off?   Are they old or sulfated?   ...
John

Don't really know how to answer the why part. The negative posts on all three is totally disconnected, and the positive is connected to a switch which is in the 'off' position.

I'd guess that the two on the coach system are at least a few years old, possibly five years old. The generator battery is about two years old. My guess is that we'll be replacing the two on the coach system at some point this spring so that we don't inadvertently run into a problem while on the road. That said, I want to make it through the winter without having to replace them while it's so horribly miserable to work outside.

[Utahclaimjumper]

 The average wet cell battery will DISCHARGE 1-2 PERCENT,,,PER DAY!!  Being at 50 percent in 30 days.>>>Dan
  You can buy the small electronic chargers for less that $20.00 each and leave them hooked up,,just check the fluid level each 90 days..

[luvrbus]

Electric scooter or wheel chair charger do a good job they are regulated and cheap to0 for a 24v charger,pay no attention to the plug end with 3 or 4 plugs there is only 2 wires they are jumped on the inside of the plug I use one on my 2-8D's 24v system it was less than 10 bucks compared to the 100 bucks for a Battery Tender  

[buswarrior]

Any "state of charge" indication on a "battery charger" is most likely a steaming pile of cow manure... useless info.

A good multi-meter is necessary for battery maintenance.

It is the voltage being applied once the battery is fully charged that convicts or dismisses the battery murderer. Too high will consume water, too low, and it isn't fully charged, and then add in the nuances of that particular battery...

As to what that voltage should be for a FLA battery... let the shouting start...

Happy coaching!
Buswarrior

[richard5933]

Any "state of charge" indication on a "battery charger" is most likely a steaming pile of cow manure... useless info.

A good multi-meter is necessary for battery maintenance.

It is the voltage being applied once the battery is fully charged that convicts or dismisses the battery murderer. Too high will consume water, too low, and it isn't fully charged, and then add in the nuances of that particular battery...

As to what that voltage should be for a FLA battery... let the shouting start...

Happy coaching!
Buswarrior

Agreed.

The charger indicated 12.5v when it initially measured the batteries. It took about an hour for it to read 100%, which was when it read 12.8v which is apparently it's preset shut-off point.

For now, I'll leave it at that and just make weekly (or bi-weekly if it stays this cold) water and charge inspections and then correct as necessary.

As a side not, we've got a spare 8D which was pulled out of our 4106 over the summer. The date tag on it indicates it was installed 10/14. Haven't touched it or charged it since September, and it showed about 12.3v when I put the charger on it. Maybe it's still got a bit of life left in it. Good to keep for a spare, if nothing else.

[luvrbus]

Multi Meters won't tell you any thing but the voltage on a battery a battery can read 12.5 and be useless as hell

[windtrader]

John mentions the use of multiple battery chargers/maintainers to keep battery banks topped off. I've been pondering this just now, if it makes sense to use two 12v chargers hooked to each set of two batteries (6v x 4 = 24 connected in series) or buy a 24 volt charger/maintainer.

[chessie4905]

I use this with a unit to charge each of the 4 batteries for 10 minutes each. They sell this as a combo now. I purchased the quad link a couple of years later. Now don't have to switch between batteries with a single charger.



https://www.pulsetech.net/xtreme-charge-4-station-quadlink-battery-charger-kit.html

[Stormcloud]

Any battery that self-discharges at the rate of 1-2% is definitely a problem. If it were my battery doing this, it wouldn't be for long. It would be back at the battery dealers place in their core pile.

Standard discharge rates for various batteries can be found here:

http://www.batteryeducation.com/2012/10/battery-self-discharge-rates.html

[bevans6]

To answer the initial question, periodic charging as you are doing is perfectly fine, won't hurt a thing, and will maintain the batteries just fine.  I do it on things like my tractor battery, and I have at least one smart charger that shuts off when the battery is topped off, and comes on again when it self-discharges to a set level (no trickle charge mode).  My smart chargers with digital readout all read 80% at anything under 100%, it's kind of a rough indicator that the battery has decent charge but isn't topped off yet. 

[TomC]

On my truck, I have 4-31 batteries for starting. I have a small solar panel (about 18" square) that I bought from CW that keeps the batteries up and charged. Recently went out and started the truck. It spun quickly, hit 2 compressions and started (Cat 3406B mechanical). This Caterpillar engine actually starts faster than my Detroit 8V-71. Good Luck, TomC