my motorguide is running out of power alot quicker than usual.any way to check which is the problem?no line behind prop...battery reads 3 volts while running motor on high,than goes back up to 12 volts a couple minutes after shutting motor off.checked battery with gravity tester and it registered good.both are almost 6 yrs old and i always chg battery when i get home .thanks for any help..

If you are reading across the post on the battery and not the cables connected to it, your battery is 100% junk. If you happen to be reading across the cables, check it again reading across the post, if it's still dropping like that, battery is junk. This is to make sure you don't have a cable that has a bad connection. A good battery should only be dropping a few tenths of a volt with motor on max.  

It would take a TM that was totally shorted and not turning at all to pull a good battery down that much, which would probably be generating a lot of smoke to go along with it.

A six yr. old battery might be the reason.

i'm reading across the battery posts so i guess it's time for a new battery,thanks

In effect, you are putting a "load test" on your battery whenever you draw power from it.  I agree with the others.  It sounds like the battery has outlived its usefulness.

Have it "load tested" at a place that sell batteries, such as an Interstate battery store.  I don't know about all of them, but the one around here does not charge for testing any type of battery.  It's a service they provide in hopes of getting your business.

Their prices are competitive as well.  An Interstate battery cost me less than a BPS battery of the same size, even with the BPS battery "on sale".