MightyMax 18Ah AGM battery

[sternwake]

OK, the results are in, and they are a little disappointing.

There is certainly some measurement error possible.

The battery was 83f
The engine was 81F, and has not been started in exactly 2 weeks.

The engine barely started on the Mightymax 18Ah agm.

upon turning the key it rolled over and slowed significantly, then chug chuged along for 2.5 seconds before catching. If a regular full size battery behaved this way i would condemn it then and there, especially considering the 83f battery temperature.

My dashboard voltmeter dropped as low as 7.83 volts
My dashboard ammeter is not set up to measure amperage on this circuit, only my main battery.

Wattmeter 1 dropped to 8.24 volts
Wattmeter 2 dropped to 9.16 volts

Wattmeter one registered 122.58 amp peak
Wattmeter two registered 82.81 amp peak

Wattmeter one registered 1010 watt peak
Wattmeter two registered 776 watt peak

The amp hour and watt hour figures were not recorded and wattmeter two just said zero for both. Wattmeter two I do not like as it always recorded Ah and WH wildly incorrectly. it is a windynation clone that came with 8awg wires.
Wattmeter one is a gtpower clone that i modified with 8awg( from 12awg)

So my '1400watt' starter consumed 1786 watts. I have never replaced it in my 17.5 years of ownership of this van. It could be original. This excessive wattage could be indications it is worn out.

Amperage wise, it consumed over 200, 205.39 amps!!

I'll have to compare readings on my regular battery monitor, but it does not record minimum voltage or maximum amperage, and does not refresh teh readings multipe times a second, perhaps twice, so it might not capture the peak amperage or minimum voltage which actually occurs.

Anyway, While I would perhaps trust this 18Ah MM AGM battery to be able to start a warmed engine in mild ambient temperatures by itself, I would not trust it to be able to start an overnight cold engine in sub60F temperatures, at least not with my existing starter which appears to be drawing significantly more wattage that it is supposed to.

The differences in wattmeter readings could certainly be different resistance on teh wiring feeding each from the battery, or the fact that wattmeter two has always been less trustworthy. The differences could be product inaccuracy too, in addition to different wire/connector resistances.

Noneof the connectors felt warm to the touch after startng the engine

My clamp on Ammeter showed the MM AGm battery accepting 11 amps at 14.7v by the time I climbed back out the side door and walked to the front of the Van.

What I found strange is that the wattmeters only read amperage in one direction. And since the alternator was providing the current, the wattmeters should have read zero. One did, but the other showed amperage flowing from battery. I unplugged wattmeter 2 and then wattmeter one showed 0.0, as it should, but then a minute later showed 0.35 to 0.65 amps flowing from battery.

i cannot explain this. I though perhaps the huge currents fried something in my wattmeters, but I then hooked them up to my one fan and it did not read current in reverse and read current in the normal load/source direction, accurately.

While I cannot say for sure my Starter was absolutely consuming 1786 watts, but I also do not believe the wattmeters are 400 watts off either. A worn starter motor should indeed draw more wattage and mine is certainly no less than 17.5 years old, and could be 30+ years old. Mine is a 1989 model year but was fabricated in Canada in june of 1988.

So anyway, there we have it. The MM battery will no doubt be able to assist my highly dischrged or weakened northstar AGM to start my engine, and could perhaps start my engine on its own if the Northstar completely failed with a shorted cell. it would depend on the battery temperature nd the engine temperature, and the condition of the battery at the time it were asked to do so. which is why I intend to keep thisbattery as healthy as possible for as long as possible by keeping it fully charged.