Can a battery tender cope with two batteries?

[College]

Hi, sorry if this is a silly question but can a battery tender be wired up to two or more batteries? In the garage i have got two bikes and a lawn mower and due to not much use over the winter I am rotating on a weekly cycle my Oxford Optimiser battery tender between the three batteries. Could I just wire it up to all three at once or will it get all confused and fry all three batteries at once? Should I not be such a tight wad and just buy two more at £35 a go?
Thanks

[WorkinMan]

I recently purchased a two bank battery tender with 2 extra 25 foot extension cords and I HIGHLY recommend it.

[boxermania]

On a tender with one set of leads it all depends on how the batteries are wired.......if the are wired in series, the current output of the tender is halved, if wired in parallel the current output will be as specified for one battery, that is if the transformer and the circuit can support the additional load.

There is only one way to find out and that is by placing a DVM (in the amp setting) in series between the charger and the first battery and then between the batteries in the series arrangement. For the parallel arrangement place the DVM between the charger and the bateries, the output should be approximately the same as if one battery was in the loop (if the charger circuit can sustain the load, as explained above).

[Sunbeemer]

There may be a problem charging two or more batteries from a single charger (even if it can handle the current load) if the batteries are different sizes (capacities). Wired in parallel, the smaller one will get fully-charged before the larger one and, if the charger is self-regulating, will convert to "float" charging before the bigger one will ever get fully charged, thus decreasing it's useful life...

[TicTac50]

My battery tender is rated at 3 amp.
Once, while on vacation, I hooked all three bikes on that battery tender, 1 amp per battery.
I don't know when the "orange" light turned "green" but all my batteries (2 with Odyssey and 1 F650cs) are fine.
I figured, let the batteries fight among them self for the extra amps they need.
About 5 years ago, while traveling long distance, the Odyssey PC680 got comletely drained, don't ask how?
I just paid 5 bucks for charging the battery at the gas station with the 10 amp charger.
5 years later same battery and still good.

[CycleRob]

If the 2 or 3 batteries are fully charged at the start from recently being run in their vehicles or having already been on the charger, it's OK to hook them all in parallel to the Battery Tender.

Here's what happens as soon as they are connected together:
They all become one big battery. No big deal. They all must be of the same design type, be it flooded cell, AGM, etc. The one that was at 12.7V will be raised up by the other 2 batteries that are at 12.9V and 12.8V. The Tender will immediately start feeding all 3 (or 2) batteries with 1.25Amps of power that will soon raise the common voltage of the group to a value higher than the highest one before the hook-up. Your Tender will just show a solid red LED for the time it takes to raise all 3 (or 2) batteries to 14.7V. It could be a few minutes if .1 Amp charging current is reached, to over 18 hours if it hasn't, but it will. Then it maintains that voltage with a solid red LED + flashing green LED for 6--8 hours. After that it will show solid green for the current controlled, permanently maintained, 13.6V float charge.


Here is a good FAQ to read.

Over this past winter my `98 Nissan truck and BMW F800ST were connected together with a (new) Battery Tender Plus. I use a specially made 14ga heavy extension cord with a cigarette lighter plug and alligator clips on opposite output ends. The truck battery has large 680 CCA capacity. The Tender has no problem getting to a steady green LED in less than a day, even when the truck's battery hadn't been driven to charge it up in about 2 weeks. Charging 3 M/C batteries wired in parallel would be a piece of cake! Just be careful with the connection's integrity and minimize any chance someone will trip on the cord(s) and yank them off. Any loose connector would have dozens of Amps of destructive power if it contacts the wrong thing.

.

[College]

Thanks every body for the advice. Looks as though some wire and crocodile clips should sort me out. Special thanks to CycleRob for the diagram that even I can follow.