LED Lenser T7 troubleshooting

I've just bought a T7 on the Internet which fails to work, I've tried 2 sets of batteries but can someone suggest anything else I should try or check before I send it back?

thanks in advance

You could try cleaning the surfaces marked by red arrows with rubbing alcohol. On most lights that have the battery holder separated from the tailcap switch, you can bypass the switch with a paper clip (I would have described it in detail if applicable) to rule it out as the source of the problem. On the LedLenser I can't think of an easy way to do that though.

I assume you checked the orientation of the batteries in the carrier? I mention this as I have an L7 that takes three AAAs and one of the batteries sits with the positive contact against the spring loaded side. I'm not familiar with the cartridge in the T7, I know it takes four AAAs, perhaps it shares the same type of layout. If you're popping the batteries in with the assumption that all of the negative terminals should be on the springs, that may be your problem. Each battery slot on the L7 is marked for polarity but they can be easily overlooked, especially if you're used to having springs being the negative contact.

If it is new just send it back,it never ceases to amaze me that people spend money and then try and fix it themselves.How strange is that.