I recently had the same warning indicator, but my amps reading was 0.2. If you're getting 5.2 amps, that would seem to be a normal reading since that's what I get when my system is running normally, or is 5.2 considered low for your cell type?

In my case, the problem was a corroded power cord. Since you eliminated all other possibilities, it would seem your cell is bad. I use the smaller SC-36 cell and they have lasted me about 4 years on average.