1999 2100i broke down yesterday

[Tomahawk18]

My wife and I went out on our boat yesterday and couldn't make it back to the dock on our own. It was our maiden voyage of the year. We installed a new battery and had the spring tune up prior to taking her out. She fired right up and purred like a kitten so we warmed her up and headed out. Engine was running great, temps were within the norms and all was good until the dash started beeping at us. I had noticed the volt meter was lower than normal on starting, but we had done some stereo work. I figured we ran the battery down a bit playing with the new speakers and the alternator would charge the batteries back up since it had started. We had only been out for about an hour and the volt meter was down even further by the time the beeping started. The stereo cut out, and I knew we were in trouble. We died a couple of minutes later and could't start back up. I am assuming the alternator has gone bad, but I guess my question is what else could be wrong?

[TeamAllen]

I'm no expert on this, but you might need to upgrade the alternator to a higher amperage?

[Tomahawk18]

Could be. We added a 2nd battery this offseason, oddly enough to try to avoid this exact issue.

[chpthril]

Give us some details about your battery setup. My guess is that something is not wired just right and one or both batteries are not getting charged.

While you where out, what position was the battery in? Did you try switch to the other battery?

You need to get in there with a DVOM and make some voltage checks at the alternator, the switch and both batteries.

[bryce2320]

My boat did this to me 2 weekends ago. I had the radio playing while I wake boarded, than the sub kept shutting off when it hit. Shut it off thinking my other battery was good but since I had switch on a and b it drained it cruising around and we were dead in the water. I upgraded to a 140 amp for $140

[Tomahawk18]

4 position perko switch set to "1 and 2" while underway. Switched to 1 and it would barely turn over (one crank) and 2 was completely dead after the alarm sounded. I will check the wiring tomorrow, but I think it is right. I will also check the alernator and battery voltages

[boatwakes]

The alternator is shot. Mercruiser part number 807653T $317, or Sierra 18-5960 65Amp output for serpentine belts, $193 at go2marine.com.

[bbethke]

For any battery problem or low voltage your first step is to get a meter and measure. You can get these for $5 at HFT or $15 at Home Depot, etc. I suggest charging up both batteries on land first and then starting up the engine (with battery switch on both). Run it up to about 1500-2000 rpm so that you know the alternator is kicking in and charging. Now measure the voltage on each battery. Since switch is on "both" both should have a voltage of around 13 volts (+/-). If less than 12.5, then that battery is not getting a charge. If not you can check the voltage between the big terminal on the alternator and ground. If this is not at 13, then the alternator is bad. If it is at 13, but low at the batteries, then you have a bad connection, missing cable, etc.

[Tomahawk18]

Confirmed... The alternator was not charging. Purchased a new (rebuilt) one and it is installed. Charged the batteries this morning. I don't have a fake a lake so I will get it in the water this weekend and make sure everything is working properly. Thank you all for your help.

[ddmracing05]

A good way for someone to test an alternator for future reference is simply get a volt meter. Charge the battery enough to get it started and running, hook up the volt meter to the battery while running and see if it reads around 12.6-13.2 and changes with throtte. Then you will know. if the volts down change at all and just go down, you need an alternator. Easiest DIY for testing the Alternator.

[Tomahawk18]

New alternator worked perfectly yesterday. All meter readings were in the ranges all of you told me they would be and the boat purred like a kitten for our 6 hours on the lake. Thanks for the advice guys.