Are my batteries any good

[teodoro50]

I bought a Catalina 27 six mos ago and have been day sailing since. No indication of age of batteries- (one starter and one house) both charge to around 12.4 V.
Sailed to the Santa Barbara channel islands, used motor for about one hour on way over and again coming back for the first hour-insurance for dodging the container ships- tried starting the motor with house battery and got nothing, starter battery worked fine though. (Yanmar 3GM)
Question is, shouldn't my house battery have enough juice to start the motor even after 1/2 hour of radar and a chartplotter operating. Any suggestions about how to test battery under load.
I don't want to but a new battery if the current one is good. Both batteries look new with no corrosion at terminals.
BTW the trip was incredible for a first experience.

[camaraderie]

12.4 volts is way low for a fully charged battery.
The simple way to test your battery condition is to go to an auto store and buy one of those "turkey baster" battery testers assuming you have wet cell batteries.
How are you charging the 2 present batteries? Is it a 3 stage charger. Does it bring the batteries to 14.2V or more when charging initially?
Lots more to ask...but get the turkey baster (hygrometer) first...about $6 bucks.

[k1vsk]

Originally Posted by windpath

RADAR + BATTERY = BAD

Take a look at your ammeter when the radar is firing, a 4KW radar draws just that, I dont run my radar without the engine on.

Regardless of the age of this discussion, there is apparently a misconception about the rating of radar power as an indication of current draw. The radar power rating (in this case, 4KW) is not an indication of current draw from the battery bank. It's more likely the 4KW radar, when transmitting, is only drawing a few amps. If, as indicated above, the amp meter indicates significantly more, the poster has a real problerm.

[camaraderie]

The power consumption of a typical 4kw radar is about 4 amps DC when transmitting.