We have become firm converts to the new generation of lithium battery powered electric outboards. The battery technology gives them plenty of endurance and enough power for most displacement tenders. We have an inverter on board so re-charging is quick and easy but I understand you can use bespoke solar chargers though these aren 't cheap. The great advantages are that they are silent, very light weight and there is no longer a need to keep petrol on board.

Our Torqeedo 1003 has, on the whole, been very reliable but, during the second season an integrated circuit board in the battery blew. The dealer arranged repair under warranty without fuss but the UK service agency proved to be slow, unhelpful and arrogant. I hope that they get this glitch sorted as it 's a great outboard.
http://www.torqeedo.com/index.php

It depends hugely on the type of tender, amount of load and speed. For instance, in our super sleek and light weight rowing boat we can easily go 6nM on one charge in flat water.

Our RIB tender is very much less efficient to row and to power. On the tender we use it at higher speeds because it 's easy enough to recharge on board Shimshal. In these circumstance a couple of miles is probably what we average but the reality is that most trips ashore in normal cruising are very short and one charge lasts for many days. The built in gps gives you real time feedback about energy consumption, speed and range so you get loads of warning of when the power is going to be cut.

Any anxieties you have about range will quickly be offset by silent motoring and the ease with which it can be passed up from tender to pushpit. It 's a very well designed piece of kit and the only caveats I have are mentioned in the first post in this thread.