Re: Voltage tester
I am 100% in agreement with the previous post but if you do not feel comfortable with a multimeter a simple 12 volt probe with a light bulb indicator will give a go/no go indication and the brightness of the bulb can give a relative indication as compared to the brightness across a fully charged battery.
By all means buy an inexpensive multimeter and learn to use it as suggested and once you have gotten comfortable with it you can buy a better one but you won't feel as bad burning up a cheap meter.
I always recommend keeping the burned out meters and hang them on the wall of your shop to remind you why it is there.

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As said,an inexpensive troubleshooting light will give you the basics but a meter is the way to go.Ron G