I have the sears pm-1 marines also and have one that is 3 1/2 yrs old and not charging to full voltage which should be around 12.8 V. Mine is reading 12.36 after sitting for 12 hrs. I made a post in the battery tech tips thread today and you can look at some info I have included from the odyssey web site , but what I have found out is that you need to use a 40 amp or better charger to recover these ....if recoverable. You can find detailed info in the odyssey web site under literature and look at the odyssey manual and also tech manual. Good reading there. The sears looks to be an odyssey 31-pcm2150 battery...so look for information on that.

Odyssey makes a 3 bank 50 amp charger specifically for these batteries that runs around $317 or so. The literature specifically said the charger should run between 14.2 and 14.7 volts when charging and anything 15 or over could make the battery vent hydrogen gas....eg specifically warning against some of those roll around automotive quick chargers that run over 15 V. I guess you should see if a sears outlet could do the 50 amp charge and then test them for you....or otherwise buy the specific charger that does 50 amp.

If you find out more or are successful , let us know the results. I did read where the batteries could sit for 2 yrs float and not need charged...eg long shelf life.

HHD