Let’s face it, there’s nothing more frustrating than preparing for and embarking on that long awaited portable outing only to discover your battery isn’t up to the job is there! If you’ve got the luxury of carrying a large battery in your vehicle then you don’t have too much to worry about, but it’s a very different story when you’ve got to carry all of your equipment in a backpack, rucksack or bicycle etc.
Finding the right compromise between battery capacity, intended power output (watts) and how long you intend being on air can be difficult. One of the biggest questions I find myself asking whenever I am out portable is how long will my small SLA battery last for? Being located in VK6 means that any DX is a long way away and running QRP when using phone is generally very challenging so I often need to up the output power a bit.
Generally, as a rule of thumb, I use the Ohms law equation P (power in watts) = E (voltage) * I (current in amperes) so for example I know that 10 watts is going to require approximately 800 Milliamps so my 9aH battery will last for plenty of time!
Bill Grahofke W2WCG, one of our Facebook group members quoted a very useful website which includes very helpful information on how to calculate information such as your battery’s runtime and it also includes a handy runtime calculator.
The PowerStream Technology runtime calculator can be accessed here and will take away some of the guesswork.