Can I test/check a Battery Tender Pro?

December 17, 2011 9:02 AM

Can I test/check a Battery Tender Pro?

I either have two bad motorcycle batteries or a bad charger.
Tender brought battery one from .9v to about 7v and won't bring it higher. Blinky lights on the tender have said the battery is "above 80% and charging" whenever connected to battery one.
When connected to battery two the tender says it's connected improperly.

I do own a multimeter, I just dont know what I'd be wanting to check.
I can't afford both a new battery and a new charger right now.
I don't have access to a known good battery.

posted by gally99 to Technology (5 answers total)

So, the bt has a voltage sensor in it. It won't supply voltage unless it sees voltage in the battery.
Thus, if battery 2 is fully discharged the bt won't recognize that it is attached. These are wet cell lead acid batteries - check to make sure each has the correct amount of acid in its cells. If any are low enough that the plates are exposed. You can try to resuscitate by adding distiller water to the affected cell.
But, when a lead acid battery gets fully discharged (which can happen simply with the passage of time with no use) it becomes permanently damaged and not able to retain a full charge.
To check the bt you can attach it to a car's battery if you have a car around - the bt cares about voltage not amperage. It will happily charge the car's battery but it will just take longer.
As to battery 1- the inability to charge above a certain voltage is a classic sign of a failed cell. Each cell in your battery provides a portion of the total voltage. Since they are wired in series the voltage you see at the terminals is the sum of the voltage of each cell.

Battery 2 is likely a goner. If you can source a new battery ask the shop to give it to you unfilled.
Check these and other links for the best ways to initialize a new battery for maximum longevity. The first charge is the most important. http://bmwmotorcycletech.info/newbattery.htm
http://dps.montcopa.org/dps/cwp/fileserver,Path,eoc/EDS/RadioSystem/Battery%20Maintenance.pdf,AssetGUID,44f8c569-a7bb-4b16-96cfd40f90207749.pdf
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

So, bottom line - yo can't use yr voltmeter to check the bt because the bt won't supply power until it sees a voltage at the leads which your vm won't supply.
Hope that helps.
posted by BrooksCooper at 9:30 AM on December 17, 2011

Response by poster: I should have mentioned, these are sealed batteries.
Thanks for the links, I'm digging into those now.
posted by gally99 at 9:42 AM on December 17, 2011

Ah - if they are sealed. Then you cannot add water, obviously. A they AGM or some other newer tech? If so - most of the above applies in any case. If you want to try to resuscitate the fully dead one get your hands on a "dumb" charger that simply supplies voltage and juice the dead one for a few hours until it shows at least 2v at the poles. At that point the bt should see it a do it's thing.

As for the one that only chars to 7v - nothing to be done to help it - if the bt won't get it to full charge nothing will. And, of course, using a 7v battery in your 12v electric system is a quick way to kill various parts of the charging system. New battery time, sadly.
posted by BrooksCooper at 10:11 AM on December 17, 2011

Oops! Spelling errors provided by ipad
posted by BrooksCooper at 10:13 AM on December 17, 2011

Many auto parts stores (Autozone etc) will do a free test on a battery to see if it's actually dead.
posted by gregr at 10:24 AM on December 17, 2011