BMW R1200RT/R1250RT Forum

I’ve always been a ‘stick it on charge full time’ maintenance routine for my bikes, but following advice from a friend (thanks Panman) I did a search and came up with this from Lifeline Batteries (US), in which paragraph 3 is particularly relevant in this cold snap.

>> Racing car, RV and even boat owners are all switching to AGM batteries due to their many advantages over their flooded battery counterparts. One of these advantages is the durability of AGM batteries, which do not require constant charging. However, how you charge your AGM battery will also play an important role in determining its lifespan.

1. Use factory-recommended chargers
AGM batteries are charger-specific. What this means is that each type of AGM battery has its own recommended chargers that have the sufficient voltage to charge them. Regrettably, using the wrong charger may result in short circuit of the battery. A big AGM battery will definitely require a big charger that will be able to match its capacity. The capacity for these AGM batteries and chargers is normally annotated in amperes. You can therefore know which the ideal charger for your AGM battery is by simply checking the recommended amperes on the battery.

2. Never partially charge AGM batteries
When it comes to devices like smartphones and laptops, partial charge does not necessarily damage the batteries. This is because they use lithium batteries. In the case of AGM batteries, lead acid is what is used, and it reacts in a different way when partially charged. All Absorbent Glass Mat batteries have to be fully charged to 100% percent in order to maintain their capacity. When you partially charge AGM batteries, they with time lose their capability to charge to full capacity. If you constantly charge your AGM battery to only 60% for instance, it may eventually fail to charge past 60%. This, in turn, reduces the lifespan of the battery.

3. Charge them in the right temperatures
Lead acid batteries can get damaged if you charge them in temperatures below 0° and above 40°. AGM batteries use lead acid, therefore, you should avoid charging them when it is too cold or too hot. Preferably, charge the batteries when the temperature range is between 0° to 40° Celsius to increase their lifespan. <<

My Ctek charger has temperature compensation and built in Sweden where they understand extreme temperatures.

I also use a CTEK with a setting for AGM batteries, but as a last resort I may even RTFM!!

Steve398 wrote: ↑Mon Dec 12, 2022 11:34 amAs a last resort I may even RTFM.

Here's a couple of nice CTEK videos.

scunny12 wrote: ↑Sun Dec 11, 2022 8:35 pm My Ctek charger has temperature compensation and built in Sweden where they understand extreme temperatures.

Just checked on my CTEK MSX 5.0, it gives optimum charging range of -20 to +50c.
However that’s only in regard to the charger not the battery itself, so I don’t really know. So I’ve sent an enquiry to Yuasa UK.

At 2:10 in the CTEK charging video, it says that the charger compensates for the ambient temperature by adjusting the voltage to protect the battery.

I asked if it was OK to keep the battery on trickle charge full time in general and particularly in this cold snap where temps are reaching -4c.

Reply from Yuasa -

Whilst it is safe to use the CTEK charger on permanently on trickle charge, it would be better practice to fully charge the battery and then monitor the voltage during storage. Provide supplementary charges when battery voltage drops to around 12.4v.
Having the battery on trickle charge will keep the acid strength high and over time will cause corrosion of internal components. By fully charging the battery you will reduce the risk of freezing but also the sulphation build up can be kept under control. 12.4v is the voltage where the sulphation process starts to accelerate. This build-up will reduce the batteries ability to accept and store charge.

Hmmm… that (sort of) makes sense. Overall I think I’ll keep it on charge, certainly in the winter, and replace it every 4 years anyway, as that appears to be about the time the batteries seem to show signs of failing. Works out about £25 a year, I can deal with that. .

Steve398 wrote: ↑Tue Dec 13, 2022 4:33 pmJust checked on my CTEK MSX 5.0, it gives optimum charging range of -20 to +50c.
However that’s only in regard to the charger not the battery itself, so I don’t really know. So I’ve sent an enquiry to Yuasa UK.

Is this any help, https://www.yuasa.co.uk/info/motorcycle ... ric%20acid.

"A fully charged Yuasa battery has a suggested operating temperature range between: -10°C to 60°C (14°F to 140°F)."

Steve398 wrote: ↑Tue Dec 13, 2022 5:17 pmI asked if it was OK to keep the battery on trickle charge full time.

The CTEK MXS 5.0 is an "all singing and dancing" charger. Once the battery is fully charged, the charger monitors the battery voltage and gives a pulse charge as required to top it up. This would suggest that it is safe to leave the charger permanently connected and switched on.

Interesting stuff.

So, if you take your car out (fitted with a lead-acid battery) in sub-zero temperatures, you disconnect the alternator to avoid charging? I don't think so!

Joking apart, I have always left my BMW's battery hooked up on "life support" (Optimate, in my case) over the winter months, when I try to avoid the salty roads. Never had any issues with premature battery failure. All systems (including "smart" chargers) have some sort of control process, more so these days than decades ago, when the good old Lucas or Bosch CVC was High Technology.

For my old 1955 Panther (6V standard lead-acid battery) I just trickle charge every 6 weeks or so (when I remember!) during the winter months. I have never paid any regard to the ambient temperature. The last battery survived for over eight years and I only changed it because I thought it was "about time" (they are fairly cheap).

Just my tuppenceworth.

Old Foxy

All the bikes I have had have always lived on a charger all year round

One bike I got 13 years on the OE battery

Only ever had one battery fail on me up to now