Charge light on.bought a new battery its dead.could it be a fuse or a bad alternator

I think I would check fuses and make sure you have good wire connections. If your battery ground is corroded or rusted badly you may have a bad connection and the battery will not charge properly. I found these link's which may apply to your situation.
Hope this will help

https://www.youtube.com/watch?v=FTGz0PKIl84

http://strongforsubaru.com/subaru-alternator-fault-fix/

Wouldn't be a fuse, but it seems as if the alternator is still not putting out normal power, or else your battery has a problem taking a charge. Better have the battery tested for a dead cell. also see what a voltmeter says about alternator output now. If you have an electrical problem in the wiring somewhere or in the alt. charging controls, then possibly one or more of the diodes in the alternator may got burnt out. That means the alternator puts out less power.
On some newer cars, the engine computer, pcm, controls the rate of charge of the alternator. So you have to be careful diagnosing -know how your system operates. That's why mechanics always ask for year, make, model, and engine size if applicable.

make sure the cables are both good if they have a spot that feels flimsy the wires inside are likely corroded and the current is not running through it properly. a simple charging system check would be recommended.

if its not charging while running at14.5 volts or so you have a charging problem mabey no power to the alternator if its charging at 14.5 or so and the batery load tests good and its going dead over night you have a draw from some component in the system.

it sounds like you have blown fuse to the Alternator.. I don't know what car you are talking about but they charging systems vary.. But if alternator isn't getting all the power it needs it won't charge. this should be checked.

good luck

that's becasue the new abattery went dead because it was not charging. The battery light must be OFF to charge the battery. Take it back to whoever fixed it. May be a bad wire betwen battery & alternator too.

check the 175 amp mega fuse in the engine compartment.

cehck this ground for a good connection - G104
Left front fender near air cleaner

check the 20 amp fuse for the charging system. Fuse 26 in teh engine compartment fuse box.

Thanks for choosing FixYa and welcome. You need to make sure the battery is holding a proper charge. Clean the terminals and clean the post. You could have a weak alternator draining your battery. You can test it by starting the car and unplugging the hot side battery terminal once the battery is charged. If it dies instantly, your alternator is bad. You may need a new battery.

You are probably correct on the bad alternator...Did your battery shop test the old battery? As you get your Mazda running again...(limited use with bad alternator) most parts stores can test the alternator output to confirm it is bad...Hope this helps.

I believe that there is a fuse in the fuse box that protects the alternator. Check all the fuses with a test light, I think you'll find that one is bad.

I dont think the dealer knew what he was doing ,your altenator has 6 diodes inside it and the are a one way check valve for current,If one fails no light will come on because it is still charging,But will drain your battery,I hope this helps you and have a merry x mas and please dont forget to vote on this solution