Battery charging question

[ShockDoc]

This might seem silly to ask- but would it be safe to use the Battery Tender Plus Gel charger that I use for my M3 to charge my winter beater non-gel battery? This battery is original equipment in my 8 yr old SUV. The temp here only peaked in the low teens today and the battery was definitely feeling it when I fired it up after work today. Or should I just get a new battery tomorrow? My priority is to avoid being stranded somewhere.

[kenwelch]

This is not the speedy reply you hoped for. Since I also use the Battery Tender charger in my class I did a little reading on their website for a battery charging lesson.

You should be able to use your "Plus" model charger on either type of battery.
In class I test the battery after fully charging. We use Midtronics and
Snap-On testers to determine the capacity of the battery.
You can often have your battery tested for free at many auto parts stores.

This is from the Battery Tender site:

OVERVIEW and COMPARISON: The Battery Tender and Battery Tender Plus battery chargers are both designed to provide a quick, economical means to recharge motorcycle and engine start batteries used in other power sports equipment. Typically, power sports engine start batteries are in the 12 Ah to 20 Ah capacity ranges. Both chargers are constant voltage type with precisely regulated output current limits. Both chargers have a regulated, nearly constant 1.25-ampere output charge current during the bulk charge phase. Physically, there is virtually no difference between these 2 chargers. Both the Battery Tender and the Battery Tender Plus operate in 3 charge modes, bulk charge, absorption charge, and float charge.

RECHARGING AGM BATTERIES: The primary difference between these 2 chargers is that the Battery Tender Plus was specifically designed to accommodate the charging requirements of the new, Absorbed Glass Matte (AGM) style batteries. To achieve that goal, it was necessary to modify the absorption charge mode in the following way. The Battery Tender switches to float mode when the charge current drops to 0.5 amps. The Battery Tender Plus switches to float mode when the charge current drops to 0.1 amps. The result is that for an extended period of time, not to exceed 8 hours, the Battery Tender Plus output voltage will be held at a constant voltage that is significantly higher than the float voltage.

With the Battery Tender, the switchover at 0.5 amp results in an absorption charge mode length of approximately 1 hour. During this 1-hour period, the battery charge voltage is held constant at a value of approximately 14.3 volts. Because of the slightly higher voltage recharge requirements of AGM batteries, and because AGM batteries require a longer period of constant voltage absorption, the Battery Tender Plus controls the output voltage at 14.4 volts while it waits for either the charge current to decrease to 0.1 amp or for the absorption charge mode control timer to expire. The end result is that the Battery Tender Plus absorption period is longer and at a slightly higher voltage than that for the Battery Tender.

Also this is from the instruction manual for your charger:

TIME REQUIRED TO CHARGE A BATTERY:The Battery Tender® Junior charges at a rate of 0.75 Amps (0.75 Amp-Hours
per hour). The Battery Tender® Plus charges at a rate of 1.25 Amps (1.25
Amp-Hours per hour). Therefore, a fully discharged 15 Amp-Hour battery will
take approximately 16 hours or 9.6 hours respectively, to recharge to 80%
capacity with a Battery Tender® Junior or a Plus. Some large automotive or
marine, deep cycle type batteries may take several days to fully recharge.

[ShockDoc]

Thank you for the information. After my original post, I went to the website and gleaned that it was safe (which I should have done before posting- but I was being lazy). I don't know the specs of the battery. The charger was in bulk mode for almost 4 hrs, then it was in float mode when I checked the next morning. It did fire up much better that morning. Given the battery age, it might be time to just put a new one in. If I were to get it tested- would you advise that I charge it fully and then have it tested?

[kenwelch]

Originally Posted by ShockDoc

.........If I were to get it tested- would you advise that I charge it fully and then have it tested?

Yes, the fully charged battery does make a difference in the test results.