The evolution of my mobile phone usage

I am not, and have never been, a huge user of the mobile phone - but consider mine to be there for "emergencies only" as I travel a fair deal, and sometimes into remote areas in South America (where, as likely as not, there will probably be no signal in any case!). I currently own a "smartphone" but it is an old one (bought in 2012) and the OS is non-upgradeable so most modern "apps" don't work on it anyway, and serves me perfectly in the capacity I use it. My only gripe is battery life!! I have to charge it daily, despite the fact some days it never gets used, and this is actually what prompted to me to make this post, but I will leave that till the end!!
I cannot remember exactly when I bought my first mobile phone, but recall it was on offer at a local supermarket and on the Orange network - it cost the grand sum of £9.99, and I think the contract was £15.00 a month - so I bought one for my wife as well. It was huge! I do not recall the brand, either, so it may have been simply an "Orange" phone. Hardly a "pocket" phone, and I do not even recall if "texting" was possible - the early phones just had a number pad, with 3 or 4 letters corresponding to each number, and you had to tap through to the letter you wanted, so it took ages to type a simple message! It didn't get used very much, in any case.
I moved over to the Vodafone network and got a Nokia 3210 after that - which was, at the time, one of the top phones! Texting was still by tapping through the numbers, but seemed easier though still slower and long-winded. It didn't really affect me, however, as my phone usage was still pretty low, and my texts were almost monosyllabic in those days!
The 3210 was good, but I found it turned itself on in my pocket, so decided I wanted a flip-phone, which would also protect the screen - and upgraded to a Motorola Razr, which really impressed my daughter as it was, at the time, pretty state of the art! I loved it! Battery life was awesome - I could get a week out of it without recharging - the keys were easy to use, the twin screen (small screen on the outside showed caller details before you answered) was great, the camera was good (for the time), and it was just a very good mobile phone.
Then Motorola brought out the Krzr, which was a slimmer version on the Razr, and I upgraded (though my contract) for one of those - and it was as good as, if not better, than the Razr! Being smaller it fit even better in the pocket, and battery life was equally as good, so I was really pleased with the swap. At the time smartphones were becoming the "norm" but I felt I didn't need all the features of those, and since the monthly contract price to get one "free" was more than double what I was paying or felt I needed, I stuck with a "regular" phone.
When I moved to Brazil in 2009 I bought a netbook, so used that for connecting to the internet when travelling - at least when overnight in hostels - so again didn't feel the need to upgrade to a smartphone, and the Krzr still fulfilled all my call and text needs, though I moved to a pre-pay (PAYG - pay as you go) contract as I was unsure of my permanence and didn't want to lock myself into a long contract.
In late 2011 I managed to crack the small outer screen on the phone, not sure how - picked it up one day and it was cracked - and tried unsuccessfully to get a replacement in Brazil, where I was at the time, and considered ordering one from the UK, but since my daughter was visiting the following year I decided to ask her to bring me a new phone, and upgrade to a smartphone!!
I have never been one for following fashions, or having to own big brand names - where style is often at the expense of quality or content - and also have never had the money to throw around updating annually just to have the latest things, even when the old ones are just as good or not worn out. This means that whenever I make a major purchase (and this had to be a sim-free, no contract phone as it would still be on a PAYG basis) I do a lot of online research first to ensure I get best value for my money!
As primarily this was going to be simply a phone, all the other features were incidental - I just wanted something that would make calls and send texts, take the odd photo (I usually carry a good compact camera so the phone's camera wasn't that important), and anything else was a bonus - but battery life was crucial! My shortlist, within my price range, was examined closely and the Samsung W i8150 was streets ahead of the competition in claimed battery life - the Samsung blurb claimed 420 hours stand-by and 120 hours talk-time - and even the independent reviews raved about how good the battery life was! So I bought one, and my daughter duly brought it out when she visited.
We travelled a bit before going to my home so the phone remained boxed up for 10 days and then I followed all the "battery conditioning" instructions before inserting my old sim-card and starting to use it in earnest.
Don't get me wrong it is a great phone - BUT the battery life is terrible! I get around 14 hours out of a full charge - when the phone is on standby and not being used at all! Using it for a couple of calls and texts (or even Whatsapp) don't seem to make any difference to battery life. I did have to change the battery (for another original Samsung one) after 3 years as the battery was "swelling" and my daughter (I was visiting the UK at the time and she is more tech-savvy than me, but I am no slouch!) warned me that smartphones do have a habit of needing regular battery replacements (not a problem generally for those who update every year or so!), but the "new" one is just as bad as the original for battery life.
What prompted me to make this post - back to the first paragraph - is that some days my phone "beeps" to tell me it has low battery (down to 15% left), while others it still has 25% life left at the same time of day when I plug it in to charge - yet yesterday it had 57% left when I plugged it in?? How does this work? The phone gets the same low to zero use every day - I probably make 2 calls a month (yes, a month!) here - to order gas or water - and the rest of the time it sits on a table next to me, so how can one day this equate to 85% battery usage, and another only 43%? I am not using GPS, which I know can use a lot of power, nor do I have it set to seek out wifi - again I have heard that if the phone is continually "looking" for internet connections this can also use a lot of power - so I cannot think of any reason why the usage should be so variable.
I may consider an upgrade soon - or a retro-grade if rumours that Motorola might release a new Razr flip - as the i8150 has another "problem" - the OS cannot be upgraded! It is running Android 2.4, so most modern apps - including some that were factory installed - do not work on it!