Not a TriMetric, but for $20 might be worth trying out...
Bayite DC 6.5V-100V Digital ammeter voltmeter Amazon suggested this for me and I'm thinking for $20 I might just give it a try. Has very good reviews too.
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The shunt goes on the negative side of the battery and the display is plenty bright. My only negative comment is the push button on the front and how it works with the display, not real intuitive, but for the money it does a good job. I checked mine for accuracy with a high quality DVM and it was pretty accurate. $16.00 and free shipping with Amazon Prime.
