pianotuna wrote:
If you MUST get an amp-hour counter use the Victron or the Smartgauge.
I have a Victron. I also have that backed up by a Simpson analog meter and a handheld Fluke that I use for calibration. All three meters measure within .05 VDC. The Victron is easy to install and takes up little space. A complete hardware mounting kit is included with the meter.
The OP's weak spot will be the small capacity of two BCI 27 series batteries. If two 6V GC2 can be installed in their place (typically, a two hour job), the OP would have twice the battery capacity and shouldn't have a worry after.