Is there an easy fix for an old iPhone 5s battery?
Battery Drop of 5% in two hours is not bad

A battery drop of 5% within two hours is not bad at all. How much does it drop throughout an entire day? How long can you use it for taking a few calls, browse a little?
If it only drops heavily, when not in airplane mode, please check your battery usage: Settings -&gt; General -&gt; Usage -&gt; Battery Usage

Replacement

Apple offers an about $80 (+ $7 shipping) battery replacement-program for iPhones https://www.apple.com/batteries/service-and-recycling/

Alternatively, if you - or a friend of you - like to fix things yourself you could consider a iFixit iPhone 5s Battery replacement kit, which is about $30 (without shipping)  https://www.ifixit.com/Store/iPhone/iPhone-5s-ReplacementBattery/IF124-002-2

iFixit provides very useful guides of how to fix electronic devices from Apple or other manufacturers.

Check warranty

You might want to also check your warranty status: https://selfsolve.apple.com/agreementWarrantyDynamic.do

If you have an AppleCare Protection Plan they might replace the battery for free!