Be aware of battery and charger inconsistencies!

[philso]

Originally Posted by sanelss

It's not that we set the charge rate to 15A, the charger states: "automatically selects charge rate from 0 to 15 AMPS to maximize battery life, charge speed and maintenance" it also makes no claims as to a rating of battery it can/can't charge. From other online documentation I found there is no danger at charging up to 1C other than shortening the battery life, which you may consider damage I suppose though. Honestly i'm no worried since we can work around it by bulk charging on 6A then cycling to these for top off

As others have already stated, the charger you are using is designed for automotive batteries where the value for C, in Amps, is much greater than the C value for the 18 Ahr batteries used in FRC. Automotive batteries rarely give an Ahr rating but they would typically be in the range of 35 to 85 Ahr. The claim about automatic charge rate selection is relevant ONLY when the charger is connected to an automotive battery. Using an automotive charger in the "automatic mode" would almost guarantee that you are charging your FRC batteries at currents well above the manufacturers recommendations for part of the time. This excessively high charging current leads to premature failure of the battery. The failure modes can consist of reduced battery capacity, shortened life and rupture of the case (possibly explosively) due to boiling of the electrolyte.

The automotive chargers use charge currents that are appropriate for automotive batteries and they change charge currents and transfer to trickle charge mode based on the battery voltage. Since the voltage at full charge is related the same for all the 12 V (nominal) batteries, irrespective of their Ahr rating, the automotive chargers are able to properly charge all automotive batteries no matter what their actual Ahr rating is.

Each week, where I work, we literally use tons of batteries just like the ones used in FRC (different Ahr rating) to build large Interruptible Power Supplies for industrial applications and data centers. These are sourced from one of the FRC legal suppliers. We CALCULATE our charging current based on the size and number of batteries in a battery bank and recommendations from the battery manufacturer. Neither we, nor any competitor that I know of, has the technology that would allow a charger to distinguish between batteries of different sizes and what charge rates are appropriate for that battery.