[LAU] [OT] digital mixer losing its presets after battery replacement

Greetings, The subject says it all. I recently had a tech replace the batteries in two Yamaha DPM11 mixers. As expected, all presets were lost, but I was able to restore them by a direct sysex transmission from one unit to the other (before that one's battery replacement). Alas, the transmitted data doesn't "keep", i.e. when the machine is turned off the battery appears to be draining its charge, because the presets are gone when I power up again. Grrrr. Also, simplesysexxer seems to receive and transmit a bulk dump with no problems, but the units do not respond correctly. The first preset gets copied, then I receive an error code "cE". I could make good use of the machine's error code definitions now, but the only service manual I found available on the net is from a private dealer who wants too much money for it. I'll try contacting a retired Yamaha tech in Toledo OH, but does anyone on these lists have an idea what I should do ? Btw, the units work fine now, they just don't keep their presets. Any & all assistance greatly appreciated ! Best, dp