Should I leave battery on charge long term?

Thread Starter

garygee

Joined Aug 7, 2018
2
I have a couple of vehicles that do not get used very often, maybe once every 6 months. They have a standard starting battery and a deep cycle auxiliary battery, which is connected via DC to DC charger. I use Ctek MXS25 chargers, and would like to know if I should leave this charger on permanently or not?
 

MrChips

Joined Oct 2, 2009
19,415
It is recommended that a lead acid battery in storage be topped up every 6 months.

If the intelligent charger has a float charge stage, then it is ok to leave the battery permanently on charge.

Check that the float voltage is 2.25V per cell, i.e. 13.50V for a 12V battery.
 

crutschow

Joined Mar 14, 2008
23,523
According to the charger data sheet it goes to a float mode of 13.6V at the end of the charge, so it should be fine to leave the charger continuously connected to the battery.
 

MrChips

Joined Oct 2, 2009
19,415
And it wouldn't hurt to measure the voltage across the battery with a DMM while still connected to the charger.
 

Thread Starter

garygee

Joined Aug 7, 2018
2
That's most helpful, thank you very much.
I'll check the voltage after 10 days, which is when it should be in float mode according to the manual.
 

crutschow

Joined Mar 14, 2008
23,523
I'll check the voltage after 10 days, which is when it should be in float mode according to the manual.
There's also a pulse-mode which it goes into after 10 days I think.
In that mode the measured voltage will likely be somewhere between the pulse mode upper and lower limits.
So you might want to check the voltage after just a few days on charge.
 

ian field

Joined Oct 27, 2012
6,539
I have a couple of vehicles that do not get used very often, maybe once every 6 months. They have a standard starting battery and a deep cycle auxiliary battery, which is connected via DC to DC charger. I use Ctek MXS25 chargers, and would like to know if I should leave this charger on permanently or not?
Generally no - I have an Optimate smart charger that throttles back to 13.6v to minimise gassing. A redundant motorcycle battery became worthless after a few years float charging.

Most battery chemistries like a bit of exercise every once in a while. recovery rates are much better on motorcycles with electric start than ones without.
 

olphart

Joined Sep 22, 2012
78
After reading enough opinions regarding off season battery maintenance, I build my own.
Simple: regulated at 13.5V, 27 ohm current limiter.
Got 13 years out of a Gates AGM, 8 out of an Interstate AGM, both motorcycle batteries.
Made several for friends for garden tractors, motorcycles, etc.
A LOT cheaper and more directly to task than commercial units.
Clip on at end of season, forget it until next season.
Meant to keep a good battery happy, can't charge / fix a soft one.

Best anecdote: 3 years on a bike in Minnesota, cleaned the carbs & it cranked right up.
Won't post my design, but it's simple enough to get close.
 
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