The problem is going to be either a bad battery, with an internal short. Or a bad voltage regulator on the engine. When batteries have shorts in them it will cause the voltage regulator to go haywire, and output to much voltage.
The other part of this is you really should not leave a charged hooked up to the battery with the battery connected to the engine. The voltage regulators on the engines are very sensitive, and can't take the constant charging like say a car with a typical alternator can. So if it does end up being a bad voltage regulator, it was the charger that likely killed it. What you would want to do is either take your battery and have it load tested, or just run the engine off of another battery. If it makes no difference then the voltage regulator would be confirmed bad at this point.
To add to that, you can still use the charger is you want to, but you would want to install a battery switch so that you can flip it and disconnect the battery from the engine when you are not using it, and then hook up the solar charger. Lastly, never run the charger or any charger and the engine at the same time. The voltage regulators are very sensitive, if it is "forced" to compete with another charger it is going to loose every time.
Does that all make sense to you?
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